7/27/2019 INPUT_OUTPUT_BASIC1.doc http://slidepdf.com/reader/full/inputoutputbasic1doc 1/137 INTRODUCTION The directory is broken down alphabetically into sections corresponding to specific classes of device. These include: • Armatures • Assistive Technologies for Special Needs • Bar Code eaders • Boards! "esks! #ads and #ens • Character ecognition • Chord $eyboards • "igiti%ing Tablets • &ye and 'ead (ovement Trackers • )oot Controllers • )orce * Tactile )eedback +,'aptic,- "evices • ame Controllers • loves • /oysticks • $eyboards and $eypads • 0ightpens • (ice • (1"1 Controllers and Accessories • (iscellaneous * 'igh "2) "evices • (otion Capture • Speech ecognition • Stylus devices: see "igiti%ing Tablets ! 0ightpens! Boards! "esks and #ads ! Touch Screens! (iscellaneous and )orce )eedback +,'aptic,- "evices. • Touch Screens • Touch Tablets • Trackballs Input DevicesAn input device is any device that is used to supply information to a computer. A few examples of input devices are given below. Keyboard The most common input device is the keyboard, which is used both for text- based data input and for selecting commands. Keyboards usually have the following: • Keys for the letters of the alphabet. • Keys for punctuation symbols.
Standard keyboard• Keys to move the typing cursor and other text controls, such as Tab,
#nsert, $elete, %ackspace, &nter, and so on.• Keys which change the function of other keys, such as 'hift, (aps )ock,
Alt, and (trl.• *unction keys numbered from *+ to *+. The function of these keys is
set by whichever program is running.
Mouse
(omputers are usually operated through a graphical user interface. Thismeans that the user selects a command from the computers screen displayby moving a pointer and clicking an icon. A mouse is the device usually usedto control the movement of the pointer on the screen.
• A mouse is used by moving it across a mouse mat or other flat surface. This moves a ball on the bottom of the mouse. The movement of theball sends a signal to the computer. 'oftware interprets this signal andperforms an operation, such as moving a cursor or drawing a line.
• A mouse has two or more buttons on top of it, the function of whichdepend upon the software being used.
• A trackball can be used as an alternative to a mouse. #t has buttons,like a mouse, but the pointer is moved using a rotating ball set into thetop of the device !basically an upside-down mouse".
• 'ome people find a trackball easier to use than a mouse. ne
advantage is that it does not need a flat area to use it. *or this reason,trackballs are sometimes included on laptop computers.
Touch Pad
• A touch pad is another device for moving the pointer. #n this case, youuse your finger or a pen-like instrument !or stylus" on a sensitive padto move the screen pointer.
• %ecause a touch pad is flat and does not re/uire the user to push downa specific key !as with a keyboard" or grasp it !as with a mouse", it isoften used as an input device for people with particular disabilities.
Touch pads are also used on laptops and palmtop computers.• Another form of touch pad is the graphics tablet. This enables the user
to create an image on the computer by drawing on the pad with aspecially designed pen. 0raphics tablets are used by graphic designartists and for childrens drawing software.
Light Pen
• A light pen is a hand-held device !very similar to a standard ballpointpen" that has a device at the tip, which either emits light or is lightsensitive. The user is able to send information to the computer bytouching the pen onto certain areas of a specially designed screen.
• )ight pens are not widely used because they re/uire a lot of armmovement, making them tiring and uncomfortable to use.
• 1ossible uses include engineering production lines and sciencelaboratories where dirt or other environmental factors make the use ofa keyboard or mouse impractical.
Joystick
• A 2oystick consists of a base and a stick perpendicular to the base. Thestick can be moved in any direction, enabling the user to move anob2ect around the computer screen. A 2oystick can perform a similarfunction to a mouse or trackball, but is only commonly used for playing
games.
Scanner
'canners are input devices used to detect a pattern on paper !pictures ortext" and then translate the pattern into computer data.
• 3and-held scanners are dragged across the paper to scan it.
• *latbed scanners have the paper placed on top of them, in a similarway to a photocopier. These are more expensive than hand-heldscanners but they are usually able to produce higher resolutionimages.
• (ompanies needing to store paper records can transfer them tomicrofilm. A microfilm is a series of page images, miniaturised onto
45mm film. 'pecial scanners are available to prepare and readmicrofilm using a computer.
• #f a scanner is used to scan a page of text, ptical (haracter6ecognition !(6" software can be used to convert the scanned imageinto text data that can be edited using word processing software.
Digital Cameras
• $igital cameras work in much the same way as normal cameras,except that the exposure from the sub2ect is recorded onto lightsensitive diodes not photographic film. The image is saved to a flash
memory card !(ompact*lash for example". #mages can often beprinted directly to a printer or displayed on a television or can betransferred to a computer !either by connecting the camera to asuitable port !such as a 7'% port" or by inserting the memory card intoa card reader.
• There are also devices to capture moving images. 8eb (ams canrecord low resolution video images. 3igh resolution digital videocameras are available, but are still /uite expensive. 'ome filmmakersare starting to record motion pictures entirely on digital video.
Any of the current types of printers satisfies the work and cost re3uirements for
someone. &ach has strengths and weaknesses. Choose your type of printer based onwhich of the features previously discussed are important to your work! then choose the
specific printer that best suits both your tasks and pocketbook.
4ith this type of printer something strikes paper * ribbon together to form a character!
like a typewriter.
Advantages:0ess e5pensive)ast (some types) Can make multiple copies with multipart paper Disadvantages: Noisy6#rint 3uality lower in some types.#oor graphics or none at all.
Types of Impact Printers
Dot Matrix
)orms characters using row+s- of pins! 7! 89! or ; which impact the ribbon on top of the paper. Also called pin printers.
The more pins! the smoother<looking the characters.
(ost dot matri5 printers have the characteristics below:
prints left to right and also right to leftTractor feed -
uses sprockets to pull continuous<feed paper Friction feed -
uses pressure to pull single sheets Advantages:1ne5pensiveCan do multi<copy forms Disadvantages:Can be slow0oudraphics of low 3uality! if possible at all
Daisy WheelCharacters are fully formed on the ,petals,! like typewriter keys.
Advantages:
Best print 3uality Disadvantages:=ery slow < > to 9> cps
2nly one font can be used at a time because you must change out the "aisy 4heel tochange fonts.
Chain and Band rinters?ses characters on a band or chain that is moved into place before striking the charactersonto the paper.
Advantages:=ery fast up to @>>> lpm (lines per minute)
Disadvantages:=ery e5pensive=ery loud
Non-Impact Printers
This type of printer does not involve actually striking the paper. 1nstead! it uses ink spray
or toner powder.
Advantages:uiet6Can handle graphics and often a wider variety of fonts than impact printers. Disadvantages:(ore e5pensive
Slower
Types of Non-Impact Printers
1nk /etSprays ink onto paper to form characters Advantages:uiet'igh 3uality te5t and graphics. Some can do color. Disadvantages:Cannot use multiple<copy paper1nk can smear
Thermal?ses heat on chemically treated paper to form characters. )a5 machines that use rolls of paper are also of this type. Advantages:
uiet Disadvantages:elatively slow&5pensive! re3uiring special paper Cannot use multiple<copy paper
#age #rinter4orks like a copy machine! using toner and a heat bar. 0aser printers are in this category. Advantages:uiet)aster than other non<impact printers! from ; to 8 ppm +pages per minute- 'igh 3uality print and graphics. Some can do color. Disadvantages:(ore e5pensive than impact printersCannot use multiple<copy paper
Thus, Things to Consider When Choosing a Printer:
'ow much output4hat speed is needed1s heavy<duty e3uipment necessaryuality of output needed0etter 3uality Near letter 3uality"raft0ocation of printer
'ow big a footprint can be handled1s loudness important(ultiple copies needed
Color print needed
What is Output?
Input
Processing
OutputStorage
Output is data that has been processed into useful form! now called Infor!ation
The Dob of a printer is to put on paper what you see on your monitor. 'ow easy this is to
do and how successfully it is done determines whether or not you are happy with your
printer choice.
(onitor screens and printers do not use the same formatting rules. 1n the olden days ofcomputers! the way something looked on the screen could be =&E different from howit would look when printed.
&arly word processors didnFt have a way to show what the printed version would looklike. Now a word processor that doesnFt have print preview! would be laughed off theshelf. (ost have a 4ES14E view! where you see almost e5actly what the documentwill look like in print! while you are still working on it.
How fast?
The speed of a printer is measured in:cps
G characters per secondlp!
G lines per minutepp!
G pages per minute
The faster the printing! the more e5pensive the printer.
Disadvantage:(ay need to separate the pages and remove the strips of perforations
$in&le $heet
Advantage:
Can change to special paper easily! like letterhead or envelopes Disadvantage:(ust add paper more often
What print ua!ity?
00etter uality Gas good as best typewriter output N0 Near 0etter uality Gnearly as good as best typewriter output"raftused internally or for a test print
A more numerical measure of print 3uality is printer resolution. (easured in dots per
inch +dpi-! this determines how smooth a diagonal line the printer can produce. Aresolution of @>> dpi will produce te5t that shows Dagged edges only under a magnifyingglass. A lower resolution than this will produce te5t with stair<step edges! especially atlarge si%es. &ven higher resolutions are needed to get smooth photo reproduction.
#rofessionals in graphics use 8>> to ;>> dpi printers.
What wi!! it print?
#rinters vary in what varieties of type they can print. Eou must know the limits of your
printer to avoid unhappy surprises6
TypefaceSet of letters! numbers! and special characters with similar design
StylesBold! italic! underlined...Si%e(easured in points
2ne point G 8HI of an inch like: 8 pt 89 pt ; pt @ pt?se 8> or 8 pt for writing a letter or report.)ontA complete set of letters! etc. in the same typeface! style! and si%eColor #rinting in color takes longer! uses more e5pensive inksHtoner! looks best on moree5pensive papers! but can add a lot to the 3uality of the outputraphics#ictures add a lot to a document! but not all printers can print graphics.
How "ig?
The footprint! or the physical si%e of a printer! determines where it can be placed.
$erial ca'le Sends data only 8 bit at a time#rinter can be up to 8>>> feet away from the computer.
(a5imum data transfer speed G 88J kilobitsHs +.88J(bitsHs-
arallel ca'le
Sends data 9 bits at a time#rinter must be within J> feet of the computer.
(a5imum data transfer speed: 88J kilobytesHs +.88J(BET&SHs-. This is 9 times fasterthan the ma5imum serial speed.
Newer printers may need 'i-directional ca'le so that the printer can talk back to thecomputer. Such a cable is re3uired if the printer can give helpful error messages. 1tFsstartling! but nice! the first time your computer politely says ,1nk is getting low, or,#lease place paper in the AutoSheet feeder.,
2ddly! 4indows K# does not support spooling for a parallel connection to a printer. Spooling is what allows you to do other things on the computer while the printeris processing and printing the document. 4inK# does spool when the printer uses a ?SB
#rinter must be within J meters +8.J feet- of the computer! when connecting straight tothe computer.LEou can hook up several J m. cables and ?SB hubs in a chain < up to J meters.M
(a5imum data transfer speed: 8 megabitsHs +8.J (BET&SHs- 0ots faster6
Best choice#
The new ?SB +?niversal Serial Bus- connection is likely your best choice! if your printercan use it. 1t is faster and a ?SB connector can be unplugged and re<plugged withoutturning off the system. ?SB ports are gradually! but rapidly! replacing parallel ports. The printer cannot handle the data as fast as the ?SB port can send it. The real limit on howfast a printer works is in how fast printer can get the characters onto the paper.
Serial cable may have to be used if a printer is shared in a fairly large office! due to thelength needed
The device which displays computer output to us has various names:
$creen
from ,computer screen, or ,display screen,
Monitor from its use as a way to ,monitor, the progress of a program
(DT
G )ideo display ter!inal from early network terminals
CRT
G cathode ray tu'e from the physical mechanism used for the screen.
G )isual display unit to cover all the mechanisms fromdesktop CTs to 0C" flat screens on laptops to 0&"screen on palmtops
$a#ing Co!ored Pictures
CRT screen:
A standard monitor screen is a CRT +cathode ray tu'e-. The screen is coated on the
inside surface with dots of chemicals called phosphors* 4hen a beam of electrons hits adot! the dot will glow.
2n a color monitor these phosphor dots are in groups of three: R ed! %reen! and Blue.This R%B system can create all the other colors by combining what dots are aglow.
There are @ signals that control the @ electron beams in the monitor! one for each Bcolor. &ach beam only touches the dots that the signal tells it to light. All the glowingdots together make the picture that you see. The human eye blends the dots to ,see, allthe different colors.
A shado+ !as, blocks the path of the beams in a way that lets each beam only light itsassigned color dots. +=ery cool trick6-
LCD screen
CD +i.uid Crystal Display- screens use an entirely different techni3ue. The screen isstill made of dots but is 3uite flat. 0C" displays are made of two layers of a polari%ingmaterial with a li3uid crystal solution in between. An electrical signal makes the crystalsline up in a way that keeps light from going through entirely or Dust partly. A black screenhas all the crystals lined up so that no light gets through.
A color 0C" screen uses groups of @ color cells instead of @ phosphor dots. The signalfor a picture cleverly lets Dust the right spots show their colors. Eour eye does the rest.
Scan Pattern
There are two patterns used by different monitors to cover the whole screen. Both scanacross the screen! in a row 8 pi5el high! from left to right! drop down and scan back left.
The non-interlaced pattern scans each row of pi5els in turn! from top to bottom. Thistype is more prone to flicker if the scan has not started over by the time the phosphor dotshave 3uit glowing from the last scan. This can make your eyes hurt or even make younauseous.
The interlaced pattern scans e)ery other ro+ of pi5els. So the odd rows are done! thenthe even rows! in the same left to right to left way. But since the rows of pi5els are veryclose together! the human eye doesnFt notice as easily if a row has gone dim before it is
rescanned. (uch friendlier to your eyes and stomach.
Light vs. Ink
Colors created by glowing dots are not 3uite the same as those created by ink on the printer. Screens use the R%B system described above. 1nks use the CM/0 system usingthe colors Cyan +a kind of blue-! Magenta +a kind of red-! /ellow! and blac0 . This iswhy what you see on your screen is not 3uite the same color when you print.
hysics esson#
Color fro! !ixin& pi&!ents# 1nk and paint make colors by the colors that they reflect. The other colors are
absorbed! or subtracted! from the light hitting the obDect. The primary colors for inks and paints are traditionallysaid to be red! yellow! and blue. 1t is more accurate to say magenta! yellow! and cyan. These cannot be created bymi5ing other colors! but mi5ing them does produce all other colors.
Color fro! !ixin& li&hts# 0ights show the colors that the light source sends out +e!its-. The colors fromdifferent light sources are added together to make the color that you see. A computer screen uses this process.The primary colors for lights are red! green! and blue<violet. (i5ed together! they can produce all the othercolors.
Color fro! optical !ixin&# The illusion of color can be created by tricking the eye. Artists of the 1mpressionist period created paintings using only dots of color. Newspaper photos are made of dots! also. The human eye blends the colors to ,see, shapes and colors that were not actually drawn with lines! Dust suggested by the dots.
Fun site1 < 0earn more from the ?niversity of Colorado! using interactive /ava applets.+/ava applets take a while to load. Eou will be happier if you have a fast computer and afast 1nternet connection.-
"esktop screens are usually 8; < 87 in. by diagonal measurement. +This is how T=screens are measured! too.- 0arger si%es are available! at a significantly higher cost.#rices are dropping! however. Resolution "etermines how clear and detailed the image is.#ictures on a screen are made up of tiny dots.8 dot on screen G 8 pixel +from ,picture element,-The more pi5els per inch! the clearer and more detailed the picture.
2ne measure of this is the dot pitch! the distance between the dots that make up the
picture on the screen. 'owever! different manufacturers measure differently. (ostmeasure from dot center to the center of the nearest same color dot. Some measure fromthe center of a dot to an imaginary vertical line through the center of the nearest dot of thesame color! giving a smaller number for the same dots as the previous method. Somemonitors use skinny rectangles instead of dots and so must use a different methodaltogether. So! dot pitch has become less useful as a measure of monitor 3uality. A dot pitch of .9 is very common and . should be good for nearly all purposes! however it ismeasured. Refresh Rate
'ow often the picture is redrawn on the monitor. 1f the rate is low! the picture will appear
to flicker. )licker is not only annoying but also causes eye strain and nausea. So! a highrefresh rate is desirable. > times per second is tolerable at low resolutions for most people. IJ times per second or more is better and is necessary for high resolutions.
Type
C%34 5%34 (%34 super (%3
"etermines what resolutions are available and how many colors can be displayed.Type
New systems now come with super =A with a picture si%e of 9>> 5 >> pi5els +as a
minimum- and 8 million colors
ColorThe number of colors displayed can vary from 8 to J to ; thousand to 8.I million.The more colors! the smoother graphics appear! especially photos.
The number of colors available actually depends more on the video card used and on howmuch memory is devoted to the display. 1t takes 9 bits to describe 8 pi5el when using Jcolors. 1t takes ; bits per pi5el when using 8 million colors. So a 02T of memory isneeded to get those millions of colors. =ideo cards now come with e5tra memory chips
on them to help handle the load.
Re)erse )ideo
e5ample:
Cursor8 ointer
The symbol showing where you are working on the screen! like: and1n the olden days of Dust "2S! there were few choices for the cursor. The invention of the blinking cursor was a tremendous event. ?nder 4indows there are a huge number of
basic to fantasy cursors to choose from. $crollin&
(oving the lines displayed on the screen up or down one line at a time
Type of %creens
Monochro!e
one color te5t on single color background! i.e. white letters on blue! or green characterson black
Color
various colors can be displayed. +This one is easy6-
The most common type of monitor! which uses a cathode ray tube.i.uid Crystal Display
6CD7?sed in laptops esp. 0arge flat monitors are becoming affordable! especially if you do nothave desk space for a large CT monitor.
las!a $creens
?sed for very large screens and some laptops. )lat! good color! but 3uite e5pensive
S pecial tasks re3uire special e3uipment.
There are a number of special<use output devices. (ore are announced every day. )romrecording earth3uake tremors to displaying CAT scans! from recording analysis in asound studio to displaying metal fatigue in aircraft structures! we have more and morespecial tasks that use computers and thus re3uire print or screen display.
"ata proDectors#roDects the image onto a wall screen
(icrofilm +C2(-Computer 2utput (icrofilmThe computer directly generates the microfilm images.
0arge )ormat #rinters?sed especially for building plans and engineering drawing and really large pictures.
#lotters use a pen to draw continuous lines and are favored for engineering drawings!which re3uire both large sheets of paper and precise lines.
SoundComputers can output voice messages! music! data as sound. 2f course you have to havespeakers and a sound card.
Quiz on Lesson 5: Output)or each 3uestion! click on the radio button for your answer. Eou will be notifiedimmediately whether your choice is correct or not. Doubling clicking may work better
?se the Back button to return to lesson pages if you want to review any information or goto the 'ome #age.
8. 4hen a computer prints a report! this output is called.
)or (ain (emory! computers use R3M! or Rando! 3ccess Me!ory. This usesmemory chips and is the fastest but most e5pensive type of storage.
Secon"ar Storage is ca##e" $u%i#iar Storage
This is what is not currently being processed. This is the stuff ,filed away,! but ready to be pulled out when needed.1t is non)olatile. +power off does not erase-
Au5iliary Storage is used for:
1nput< data * programs2utput< saving results of processing
So! Au5iliary Storage is where you put last yearFs ta5 info! addresses for old customers! programs you may or may not ever use! data you entered yesterday < everything that isnot being used right now.
2f the various types of Au5iliary Storage! the types used most often involve some type
of !a&netic dis, . These come in various si%es and materials! as we shall see. Thismethod uses magnetism to store the data on a magnetic surface.3d)anta&es#
high storage capacityreliablegives direct access to data
A dri)e spins the disk very 3uickly underneath a read8+rite head! which does what itsname says. 1t reads data from a disk and writes data to a disk. (A name that actuallymakes sense!)
$tora&eIntro
'a$netic Dis(s
Dis( FormatDis( )apacity
ccessin$ Data
)arin$ &or Dis(s
)arin$ &or Data
'a$netic Tape
Optical Dis(s
Other Devices
Quiz
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Types of $agnetic 'is#s
Dis,ette 8 Floppy Dis,
Si%es:
JO,
@P,
Both si%es are made of mylar with an o5ide coating. The o5ide provides the magnetic
3uality for the disk. The ,floppy, part is what is inside the diskette covers < a very floppy piece of plastic +i.e. the mylar-
Other Re!o)a'le Media
Several other kinds of removable magnetic media are in use! such as the popular Qip disk.All of these have a much higher capacity than floppy disks. Some kinds of newcomputers come without a floppy disk drive at all.
&ach type of media re3uires its own drive. The drives and disks are much more e5pensivethan floppy drives and disks! but then! you are getting much larger capacities.
"ard Dis,s
These consist of 8 or more metal platters which are sealed insidea case. The metal is one which is magnetic. The hard disk isusually installed inside the computerFs case! though there areremovable and cartridge types! also.
Technically the hard dri)e is what controls the motion of thehard disks which contain the data. But most people use ,harddisk, and ,hard drive, interchangeably. They donFt make thatmistake for floppy disks and floppy drives. 1t is clearer with floppies that the drive andthe disk are separate things.
All magnetic disks are similarly for!atted! or divided into areas! called
trac,s
sectors
cylinders
The formatting process sets up a method of assigning addresses to the different areas. 1talso sets up an area for keeping the list of addresses. 4ithout formatting there would be
no way to know what data went with what. 1t would be like a library where the pageswere not in books! but were scattered around on the shelves and tables and floors. EouFdhave a hard time getting a book together. A formatting method allows you to efficientlyuse the space while still being able to find things.
Trac#s
A trac, is a circular ring on one side of the disk. &ach track has a number.The diagram shows @ tracks.
%ectors
A dis, sector is a wedge<shape piece of the disk! shown in yellow. &ach sector isnumbered.2n a JO, disk there are 9: tracks with 7 sectors each.
2n a @P, disk there are ;: tracks with 7 sectors each.
So a @P, disk has twice as many named places on it as a JO, disk.
A trac, sector is the area of intersection of a track and a sector! shown in yellow.
C!usters
A cluster is a set of track sectors! ranging from to @ or more! depending on theformatting scheme in use.
The most common formatting scheme for #Cs sets the number of track sectors in acluster based on the capacity of the disk. A 8. gig hard drive will have clusters twice aslarge as a J>> (B hard drive.
< cluster is the !ini!u! space used by any read or write. So there is often a lot of slac,
space! unused space! in the cluster beyond the data stored there.
There are some new schemes out that reduce this problem! but it will never go awayentirely.
The only way to reduce the amount of slack space is to reduce the si%e of a cluster bychanging the method of formatting. Eou could have more tracks on the disk! or else moresectors on a track! or you could reduce the number of track sectors in a cluster.
2n a double<sided floppy! a track from the top surface and the same R track from the bottom surface of the disk make up a cylinder. The concept is not particularly useful forfloppies.
2n a hard disk ! a cylinder is made of all the tracks of the same R from all the metal disksthat make up the ,hard disk,.1f you put these all together on top of each other! youFd have something that looks like atin can with no top or bottom < a cylinder.
The computer keeps track of what it has put where on a disk by remembering theaddresses of all the sectors used! which would mean remembering some combination of
the cylinder! track! and sector. Thank goodness we donFt have to remember all thesenumbers6
4here the difference between addressing methods shows up is in the time it takes for thereadHwrite head to get into the right position. The cylinder method writes data down thedisks on the same cylinder. This works faster because each metal platter has a readHwritehead for each side and they all move together. So for one position of the readHwrite heads!the computer can put some data on all the platters before having to move the heads to anew position.
What happens when a dis# is formatted?
8.All data is erased .
Don't forget this!!
. Surfaces are checked for physical and magnetic defects.
@.A root directory is created to list where things are on the disk.
The capacity of a magnetic disk depends on several factors.
4e always want the highest amount of data stored in the least possible space. (Peopleare so greedy this way!) So the capacities of storage media keep increasing while costkeeps decreasing. 1tFs a lovely situation for the user6
Capacity of a 'is# depends on:
<* = of sides used#
single-sided
double-sided
>* Recordin& density <
how close together the bits can be on a track sector of the innermost track
Advances in technology for the readHwrite head and for the densities on the disks are bringing larger and larger disk capacities for about the same price. 1n fact! you cannotfind a small capacity drive to buy! even if you wanted one6 8> B drives are plentiful+(arch. >>@- and for the same price that we used to buy 8 ig drives +under >>-. 1tFsenough to make you cry to think of what we paid over the years and what we could getfor those dollars today. Ah! well. ThatFs the way the computer world works6
Touch the mylar Bend#ut weight on disks.Spill on it
'sing (#opp Disks
1mproper preparation or use of a floppy disk can ruin your day! and even your floppy
drive. A few pointers are in order.
?se standard co!puter dis, la'els. Note that some labels wrap across the top as pictured at the right. 2thers fit entirely on the front of the disk.
Write on the label66 1f your disks are not kept strictly at home! every label should include
your name and something about whatFs on the disk. +2n JO, disks! use a felt<tip markeronly. A pen or pencil can damage the disk inside.-
$eal all edges down firmly. A loose corner might stick to the inside of the floppy drive!creating a maDor mess in there.
#ut the label in the ri&ht spot. "onFt cover the holes in the corners of @P, floppies. "onFtstick to the metal slide .
(ost important! insert the floppy ri&ht side up6 The label goes on top! the round metal part is on the bottom. The edge with the metal slide goes in first.
There are fewer precautions for hard disks since they are
more protected by being sealed in air<tight cases. But whendamage does occur! it is a more serious matter. 0argeramounts of data can be lost and hard disks are much! much
more e5pensive that floppy disks.
'ard disks can have problems from magnetic fields and heat like floppies do! but theseare very rare.
(ost problems occur when the readHwrite head +looks like a pointer in the photo-damages the metal disk by hitting or even Dust touching it. This is called a head crash.
4hen the computer is on! the hard disk is spinning e5tremely fast. Any contact at all cancause pits or scratches. &very scratch or pit is lost data. "amage in the root directory
turns the whole hard disk into a lovely doorstop6 1tFs completely dead.
So the goal here is to keep that readHwrite head where it belongs! Dust barely above thehard disk! but never! ever touching it.
Don&t
/ar the computer while the disk is spinning.
Turn the computer off and 3uickly back on before spinning has stopped.
Besides protecting the physical medium you are using to store data! you must also
consider what you can do to safe&uard the data itself. 1f the disk is kept from physicalharm! but the data gets erased! you still have a maDor problem.
So what can you do to safeguard the data on which you rely
Write protect This keeps your files from being overwritten with new ones.)or floppies! you do this physically:
JO, G cover the 4rite #rotect notch with tape
@P, G open the 4rite #rotect slide
)or hard disks! make files ead<2nly andHor 'idden to keep them from beingoverwritten. This is done by changing the file attributes using whatever system you havefor managing files.This is useful only for files you wonFt be altering later.Bac,up
(ake multiple copies of important data often. The more important the files are! the more
copies in more places you need.3nti)irus
?se an antivirus program continuously.
Co!puter )iruses are sneaky computer programs that can erase your data and even yourwhole system. (ost viruses are merely annoying and are created as practical Dokes. Butthere are a number of very damaging viruses out there.
Eour computer gets a virus by downloading an infected file from the internet or youroffice network! or by first using a floppy in an infected computer and then accessing afile on that floppy with your own computer. This makes it difficult to keep a virus from
spreading.
2nce you have disinfected your computer! it can get re<infected from a floppy that wasused between the time you were infected with the virus and when you disinfected it. Anumber of nasty viruses hide for 3uite a while before doing their nasty things. So you caninfect a lot of your own backups and other disks and spread the infection! allunknowingly! to others. So run an antivirus program that actively looks for viruses all the
time. "onFt wait until you have symptoms. A lot of damage can be done before you figureout that you have a virus.
Ma&netic tape uses a method similar to that of =C tape for storing data.
The speed of access can be 3uite slow! however! when the tape is long and what you wantis not near the start. So this method is used primarily for maDor backups of large amountsof data.
Businesses especially might do a backup of the dayFs transactions every day and a backupof the whole system once a week or so. $eeping sets of backups like this minimi%es theamount of data loss when the computer system goes down.
Types of Tape
&ach different tape storage system has its own re3uirements as to the si%e! the container
type! and the magnetic characteristics of the tape. 2lder systems designed for networksuse reel<to<reel tapes. Newer systems use cassettes. Some of these are even smaller thanan audio cassette but hold more data that the huge reels. &ven if they look alike! themagnetic characteristics of tapes can vary. 1t is important to use the tape that is right forthe system.
Tape eelTape Cassette
Tape &ormats
/ust as floppy disks and hard disks have several different formats! so do magnetic tapes.
The format method will determine the following characteristics.
Characteristic
oo,s li,e#
Density 'igher density means more data on shorter tape(easured as 'pi G 'its per inch ranges from 9>> bpi up to J> bpi
Bloc,s The tape is divided into logical blocks! as a floppy is divided into tracks andsectors. 2ne file could take up many logical blocks! but must take up one whole block at least. So smaller blocks would result in more room for data.
%ap
Two kinds of blank spots! called gaps! are set on the tape.Inter'loc, &ap which separates logical blocks.Interrecord &ap which is wider and separates records.
Notice the two si%e lines cutting across the tape in the picture above. Smaller gaps wouldallow more data to be stored on the same si%e tape.
An entirely different method of recording data is used for optical dis,s. These include
the various kinds of C" and "=" discs.
Eou may guess from the word ,optical, that it has to do with light. EouFd be e5actlyright6 0aser light! in fact.
2 ptical disks come in several varieties which are made in somewhat different ways for
different purposes.
)o* optica# "isks are simi#ar
• )ormed of layers
• "ata in a spiral groove on starting from the center of the disk
• "igital data +8Fs and >Fs-
• 8Fs and >Fs are formed by how the disk absorbs or reflects light from a tiny
The different types of optical disks use different materials and methods to absorb andreflect the light.
)o* It +orks ,a simp#e version-
An optical disc is made mainly of polycarbonate +a plastic-. The data is stored on a layerinside the polycarbonate. A metal layer reflects the laser light back to a sensor.
To read the data on a disk! laser light shines through the polycarbonate and hits the datalayer. 'ow the laser light is reflected or absorbed is read as a 8 or a > by the computer.
1n a C" the data layer is near the top of the disc! the label side.
1n a "=" the data layer is in the middle of the disc. A "=" can actually have data in twolayers. 1t can access the data from 8 side or from both sides. This is how a double<sided!double<layered "=" can hold ; times the data that a single<sided! single<layered "="
can.
!ateria#s
The materials used for the data +recording- and metal +reflecting- layers are different fordifferent kinds of optical disks.
+%rite/ erase/ %rite a$ain-Phase"chan$in$ metal alloy &ilm
luminum
Rea" On#:
The most common type of optical disk is the CD-ROM! which stands for Co!pact Disc
- Read Only Me!ory. 1t looks Dust like an audio C" but the recording format is 3uitedifferent. C"<2( discs are used for computer software.
D(D used to stand for "igital =ideo "evice! but now it doesnFt really stand for anythingat all6 "="s are used for recording movies. The C"s and "="s that are commercially produced are of the Write Once Read Many +WORM- variety. They canFt be changed once they are created.
The data layer is physically molded into the polycarbonate. its +depressions- and lands +surfaces- form the digital data. A metal coating +usually aluminum- reflects the laserlight back to the sensor. 25ygen can seep into the disk! especially in high temperaturesand high humidity. This corrodes the aluminum! making it too dull to reflect the lasercorrectly.
C"<2( and "="<2( disks should be readable for many! many years +8>> >>-! but only if you treat them with respect.
+rite Once:
The optical disks that you can record on your own computer are CD-R ! D(D-R ! andD(D@R discs! called +rita'le or recorda'le dis,s.
The metal and data layers are separate. The metal layer can be gold! silver! or a silveralloy.
%o for the %old# old layers are best because gold does not corrode. Naturally! the best is more e5pensive. Sulfur dio5ide can seep in and corrode silver over time.
The data layer is an organic dye that the writing laser changes. 2nce the laser modifiesthe dye! it cannot be changed again. 4rite 2nce6 ?ltraviolet light and heat can degrade
the organic dye.
(anufacturers say that these disks have a shelf<life of J < 8> years before they are usedfor recording. There is no testing yet about how long the data will last after you record it.'umph6
A writable disk is useful as a backup medium when you need long<term storage of yourdata. 1t is less efficient for data that changes often since you must make a new recordingeach time you save your data. #ricing of the disks will be important to your decision touse writable disks.
Re*rite:
An option for backup storage of changing data is re+rita'le dis,s! C"<4! "="<4!"="4! "="A(.
The data layer for these disks uses a phase<changing metal alloy film. This film can bemelted by the laserFs heat to level out the marks made by the laser and then lasered againto record new data.
1n theory you can erase and write on these disks as many as 8>>> times! for C"<4! andeven 8>>!>>> times for the "="<4 types.
(d)antages of Optica! 'is#s
8. hysical# An optical disk is much sturdier than tape or a floppy disk. 1t is physically harder to break or melt or warp.. Delicacy# 1t is not sensiti)e to being touched! though it can get too dirtyor scratched to be read. 1t can be cleaned6
@. Ma&netic# 1t is entirely unaffected 'y !a&netic fields.
;. Capacity# 2ptical disks hold much more data than floppy disks.
#lus! the non<data side of the disk can have a pretty label6
)or software providers! an optical disk is a great way to store the software and data thatthey want to distribute or sell.
8. Cost# The main disadvantage has been cost.The cost of a C"<4 dri)e has dropped drastically and 3uickly. 1n 877J such adrive was around @>>>. 1n the summer of 877I C"<4 drives were down to Dust
under 8>>>. 1n (arch >>@ a C"<4 that will read at ;>K speed! write on C"< media at ;>K speed! and write on re<writable media at 8K! can be bought forunder 8>> ?S66
The cost of dis,s can add up! too. ecordable disks +one time only- cost about.@> ?S each +(arch >>@-. e<writable disks cost about .; to .9J each.
So for commercial use! the readHwrite drives are 3uite cost effective. )or personaluse! they are available! but may not be 3uite yet cheap enough to use for datastorage for everyone.
. Duplication# 1t is not as easy to copy an optical disk as it is a floppy disk.Eou need the software and hardware for writing disks6 +This is an advantage asfar as commercial software providers are concerned6- This is balanced by the factthat it is not as necessary to have e5tra copies since the disk is so much sturdierthan other media.
Care of Optica! 'is#s *C's, '+'s
Eour C"s and "="s are not going to last forever. They certainly store data longer than
floppy disks6 (is<handling your optical disk can 3uickly make your data unreadable.&ven fingerprints can do damage over time.
• 2nly open a recordable disk Dust before you plan to record on it.
• After recording! make sure the disk works as you e5pect: ead dataU run
programs.
1nvention springs eternal in the computer industry. So more and different devices are brought out all the time! especially for special uses.
The history of computing suggests that some new technology will take over the market inthe near future. uessing which one will win the race is what makes fortunes in the stockmarket6
Flash Me!ory Several different brands of removable storage cards! also called
memory cards! are now available. These are solid-state devices+no moving parts- that read and write data electrically! instead ofmagnetically.
"evices like digital cameras! digital camcorders! and cell phones may useCompact)lash! Smart(edia! or another flash memory card.
0aptop computers use #C(C1A cards! another type of flash memory! assolid<state hard disks.
U$B dri)e This new type of flash memory storage device does not
yet have a generally accepted name. &ach company callsit something different! including flash pen! thumb drive!key drive! and mini<?SB drive.
All are small! about the si%e of your thumb or car key! and plug into a?SB port on the computer. No drivers are needed for 4indows K#! >>>!or (e. #lug it in and the computer reports a new hard drive6
Such small flash drives can have storage capacities! from 9 to J (B6(uch better than a floppy disk6
Some flash drives include password protection and the ability to runsoftware right off the ?SB drive. So cool6
Re!o)a'le hard
dri)es
Several types of special drives that compress data areavailable. A regular e5ternal hard drive can be used for backup! too.
The image at the right is of an e5ternal Qip drive with a disk sticking out.
Mass stora&e Businesses with very large sets of data that need easy access use sets ofcartridges with robot arms to pull out the right one on command.
$!art cards A chip on the card itself tracks changes! like deducting purchases from the amount entered originally on thecard. Smart cards are already used in &urope and atcolleges instead of using a handful of coins at vending
machines and at laundromats.
Another use involves a new sensor technology which lets a smart cardread your fingerprint right on the card. The digital image of the fingerprint
is then transmitted to a database to compare it with the one on file for thatcard. Eou can prove you are really you66
Optical cards A chip on the card holds information like health records and auto repairrecords. They can hold more data than the smart cards since they donFtneed to do any processing.
Quiz on Lesson : Storage
)or each 3uestion! click on the radio button for your answer. Eou will be notifiedimmediately whether your choice is correct or not. Doubling clicking may work better
?se the Back button to return to lesson pages if you want to review any information or goto the 'ome #age.
Co!puter co!!unication is the transmission of data and information over acommunications channel between two computers! which can be several different things.
Communications between computers can be as simple as cabling two computers to thesame printer. 1t can be as comple5 as a computer at NASA sending messages through anelaborate system of relays and satellites to tell a computer on (ars how to drive aroundwithout hitting the rocks.
"epending on the conte5t! for computer communications you might use the terms:
Data Co!!unications for transmission of data and information over a communicationschannel
Teleco!!unications for any long<distance communications! especially television
Teleprocessin& for accessing computer files located elsewhere
A communications channel! also called a communications line or lin, ! is the path thatthe data follows as it is transmitted from one computer to another. Below is an animationof a communications channel at work. A #C is sending a message to a host computerclear across the country. Notice the variety of transmission methods used: telephonelines! satellite links! microwave relay. This is a si!plified version of what really goes on6(he animation runs " times and stops# o restart it$ use your browser's %efreshcommand#)
+round insulated wire- Advantage: Not susceptible to interferenceTransmits faster Disadvantage:'eavy * bulky Needs booster over distance
Fi'er optic line
+glass fibers- Advantage:Smaller
0ighter)aster (speed of light!) No interference Disadvantage:&5pensive'arder to install and modify
0roa"cast
)or longer distances or when cables are not practical! other transmission media come
into play. 4eFre getting really high tech here6
1t may seem odd to call microwaves! radio waves! or light a ,physical, medium. All areelectromagnetic in nature. Sometimes they are treated by scientists like streams of teeny!tiny particles and other times like waves on the beach. 1n their ,particle, life! they do behave like a bunch of physical particles. So itFs not 3uite as odd as it first appears. (&utall those electromagnetic things are plenty odd!)
Wireless
+infrared! light! radio- Advantage: )le5ible#ortable Disadvantage:SlowerSubDect to interference
An analo& si&nal uses variations +modulations- in a signal to convey information. 1t is particularly useful for wave data like sound waves. Analog signals are what your normal phone line and sound speakers use.
$odems
2ften communications between computers use the telephone system for at least part of
the channel. A device is needed to translate between the analog phone line and the digitalcomputer. Such a device is the !ode!! which comes from ModulateHDe!odulate! whichis what a modem does. 1t modulates a digital signal from the computer into an analog oneto send data out over the phone line. Then for an incoming signal it demodulates theanalog signal into a digital one.
Though rather small! modems are very comple5 devices. There are entirely too manycommands! protocols! and configuration choices available. 2nce you get a modem set upand working right the first time! you probably wonFt have to tinker with it muchafterwards. 'urrah66
Transmission Rate
Confusion abounds when it comes to measuring the transmission rate of a modem.Throu&hput is the term for the entire process < how much data is moved during a certainamount of time. Since the modem is only part of the process of moving data! getting afaster modem may not speed up your data transfers.
There are two different parts of the data transfer to measure: the digital process and theanalog process.
Di&italThe rate of digital transmission is measured in 'its per second +'ps-. Common rates for
regular modems are 9.9 $bps! @@. $bps! and J $bps where the $ stands for thousand.Completely digital devices +discussed below- are much faster. )aster is better! of course.;>> bps would send a ><page single<spaced report in J min. (his is *!!)
3nalo&The analog side is measured in 'aud where 8 baud is one change in the signal persecond. (ost people use bps and baud as though they were the same. )or speeds of ;>> bps and under! this is true! but is it not so for the higher speeds where more than one bit istransmitted per signal change.
Phsica# tpes
There are three physical types of modems:
5xternal
which plugs into a serial port on the back of the computer
Advantages:Can be moved to a different computer easily."oes not take up a slot inside the computer.0ights on front are visible to show what the modem is doing. Disadvantages:Takes up deskspace.Adds more cables to the tangle.
Internal
where the phone line plugs directly into card through the back of the computer Advantages:Saves deskspace.Saves a cable. Disadvantages:e3uires an internal peripheral slot. (hey get filled up#)(ust use software display to see the lights that show what the modem is doing.
3cousticalwhere the telephone handset is placed into the device! which is connected to the computer+2ld technology6 Not many of these around any more.- Advantages:Can use a phone without having to move the phone wire. Disadvantages:Bulky.Connection much more prone to static and interference.2nly a standard handset will fit.
'igita! $odems
A digital modem does not have to convert between analog and digital signals.Technically itFs not a ,modem, at all since it is not modulating and demodulating. Adigital modem is faster than an analog modem.
To get the increase in speed you will have to pay e5tra +of course6-. "igital modems aremore e5pensive and so are digital data lines from the phone company. The phone
company has to install additional e3uipment for some kinds of digital modems.
Normally a digital modem can receive data at a much higher rate than it can send it out.That works out fine for most people because they are only sending out a few responsesinstead of whole web pages or data files.
*arning: nce you have used a high speed device$ you will be spoiled forever!
Types of Di&ital Mode!s
I$DN !ode!
+Integrated $ervices Digital Network- < a digital device using a digital phone line. 1tactually should be called a ter!inal adapter! but the name modem has stuck. An 1S"Ndevice is capable of higher rates than an normal modem! ; $bps for a single line and89 $bps for a bonded dual line. 1S"N adapters cost more than normal modems and alsore3uire special arrangements with the phone company (and more ++ for them$ of course!).)iber optic line is best for the highest 1S"N transmission rate! but the copper wires usedin most homes and offices will work also.
,ote: o get the highest speeds out of your -D, modem$ you'll need a high speed -.(input.output) card in the computer to which to connect the modem#
Ca'le !ode!
'ooks up to your cable T= line and can receive up to 8.J (bps. Eou must have cable T=
service with a cable company that also provides data service. Eou will need a specialcable bo5 to which you connect your T= and your computer. Eou will be sharing the linewith all of the cable customers hooked up to your particular cable line. The actual transferrate you get will depend on how many people are using the cable at the same time. 2ncecable modems become popular in your neighborhood! your speed will slow downnoticeably. 1t will probably still be faster than 1S"N.
3D$
+3symmetric Digital $ubscriber ine- < a new technology that allows a single regulartelephone line to serve for normal phone calls and digital data at the same time. AnA"S0 modem receives data at rates ranging from @9; $bps to 9(bps! depending on the
particular kind of service. &ven the slowest type is ; times faster than the best 1S"N6Besides great speed! A"S0 does not re3uire a separate phone line and you are connectedall of the time. No more dialing up6
Eou can use a regular phone on the same line and at the same time that you are surfingthe 1nternet. No more busy signals to your friends and relatives6 Another plus is that youcan easily hook up all of the new parts yourself. This saves a 02T of aggravation sinceyou wonFt have to wait on the phone company or the cable T= guy to show up.
"o+ De)ice $peeds Co!pare
The table below will help you see Dust how much faster the different transfer rates are. Toread the table! look at the speed in the top row! which is in kilobytes per second. Below ityou will see how long it takes to transfer 8 (B! 8> (B! and 8>>> (B at that speed.Check out the last row. This one really shows the difference between analog modems andthe digital kind. The times go down from days to hours or even minutes6
emember that Dust because your device is a'le to send and receive at a certain rate doesnot mean that it will ever actually work that fast. There are many other factors in thecommunications channel that can reduce the transmission speed from the ma5imum.
Protoco!s
To talk to each other! modems have to e5change a good bit of information! since there
are so many different types and speeds of modems around. ThatFs what the high pitcheds3ueals and s3uawks are that you can hear when an analog modem is trying to connect.1tFs modem talk for ,So! who are you "o you speak my language 4ell! maybe we canfind a common language so these guys can get connected.,
A digital modem does not make noises +an advantage6- but it must do the same kind ofnegotiation with the device at the other end to come up with a common language! called a protocol.
A protocol defines what information is e5changed and in what order. The names of the
protocols are of the form )*==. So youFll see things like v.Jbis! v.@;! and v.8>. Some protocols are more stable or faster than others at certain tasks.
Eou canFt Dust hook up your computer to a network or a modem and start sending and
receiving data. The computer needs instructions on how to do this. Eou need some kindof co!!unications soft+are. Since there are a number of different communicationstasks! there are different kinds of programs that manage those tasks.
Co!puter to Co!puter
Intro
Transmission 'e!ia'o!ems
So&t%are Net%or(s
Net%or( )on&i$urations
Net%or( Servers
Quiz
Home
Glossary
Search
Next Lesson
'ia!ing
"ialing software tells the computer how to place a call on the phone line connected to it.
1t also displays messages about the progress of the call or lack thereof. A list of phonenumbers for fre3uently called! or fre3uently forgotten! numbers is an important feature.
These capabilities are often included in other software packages.
&i!e Transfer
2ne of the most common uses of computer to computer communications is to transfer
files from one to the other.
Do+nloadin& means to transfer a file to your computer fro! elsewhere.
Uploadin& means to transfer a file fro! your computer to another.
#rograms that manage this process include many file management features. Eou need to be able to see what files are available! their si%es! and the folders you can put thetransferred file in. Eou may want to rename the file or create a new folder for your newfile.
Such a program will also handle the process of connecting to the other computer. (anyof the names of these programs include the letters FT! which stands for File Transfer
rotocol. (/es$ another kind of protocol# And there are more!!)
Termina! mu!ation
#rograms running on a network or that connect to a computer bulletin board +BBS-!
make an assumption about what kind of keyboard is being used. $eyboards for terminals
used on networks often have assigned special functions to certain keys. They may evenhave keys that donFt e5ist on standard keyboards. 1n order to work with the network programs! you need a program that will disguise your keyboard and make the networkthink that you are one of them6 Eou must e!ulate! that is mimic! the keyboard that ise5pected.
4hen sending data over a communications channel! there is always the possibility that
someone will see your data that you didnFt mean to. 1f your data is of a sensitive nature!like your credit card number! or if it is secret! like the formula for Coca<Cola! youFd probably like to keep strangers from reading it.
A data encryption program encodes your data! Dust like spies do. So to read it! a person
would need the right decoding program and the right password or file to give that program so it would know what to do e5actly.
A net+or, is a set of computers which are linked together on a permanent basis. This
can mean two computers cabled together on the same desk! or thousands of computersacross the world.
Advantages:&nables users to share hard+are like scanners and printers. This reduces costs byreducing the number of hardware items bought.
Allows users access to data stored on othersF computers. This keeps everyone up<to<dateon the latest data! since itFs all in the same file! rather than having to make copies of thefiles! which are immediately out<of<date.
Can even let users run pro&ra!s that are not installed on their own computers but areinstalled elsewhere in the network. This reduces the effort for networks administrators tokeep programs configured correctly and saves a lot of storage space. Disadvantages:
Accessing anything across a network is slo+er than accessing your own computer.
More co!plexity adds new problems to handle.
ess custo!i2ation is possible for shared programs and folders. &veryone will have to
follow the same conventions for storing and naming files so others can find the right files.
Sharing is hard for some folks!
.(N
A 3N is a ocal 3rea Net+or, . This would include networks where the computers arerelatively close together. So 0ANs would be within the same office! a single building! orseveral buildings close together.
The graphic at the right shows two buildings with ; departments connected as a 0AN.
W(N
A W3N is a Wide 3rea Net+or, ! which would be all networks too large to be 0ANs.There doesnFt seem to be a clear line between the two designations. A 4AN would bemost useful for large companies with offices or factories in widely separated areas! like(icrosoft! 1B(! )ord! AT*T! etc.
There are a number of ways that computers can be connected together to form net+or,s.
The pattern of connections depends in part on the distances involved since thatdetermines what hardware must be used. 1t also depends on the degree of stability neededfor the network. That is! how important is it that the whole system canFt crash at the sametime. These choices carry dollar costs! too. Better costs more! sometimes a 02T more.
&ach device in the network! whether itFs a computer! printer! scanner! or whatever! iscalled a node.
%tar
The star pattern connects everything to one host! which is the computer that handles the
network tasks and holds the data. All communications between computers go through thehost. This configuration is good for businesses that have large amounts of rapidlychanging data! like banks and airline reservation offices. Advantages:ives close control of data.&ach #C sees all the data.?ser sees up<to<date data always.1f a computer other than the host fails! no other computer is affected. Disadvantages:1f host computer or its software goes down! the whole network is down.(A backup computer system would be necessary to keep going while repairs are made#)
/usThe 'us pattern connects the computer to the same communications line.
Communications goes both directions along the line. All the computers can communicatewith each other without having to go through the server.
Advantages:Any one computer or device being down does not affect the others. Disadvantages:CanFt connect a large number of computers this way. 1tFs physically difficult to run theone communications line over a whole building! for e5ample.
0ing
The rin& pattern connects the computers and other devices one to the other in a circle.
here is no central host computer that holds all the data. Communication flows in onedirection around the ring. This configuration is good when the processing of data can be
done on the local #C.
Advantages:e3uires less cabling and so is less e5pensive. Disadvantages:1f one node goes down! it takes down the whole network.
1n the to,en rin& form of a ring network! a token is constantly passed along the network.A device must wait until the token is at that device. Then it can attach the message itwants to send to the token. 4hen the token reaches the intended recipient device on thenetwork! it will release the message. The token circulates very fast! but this obviously
means that most of the time a device will have to do some waiting before it can send outa message.
Connecting Networ#s
Networks can be connected to each other! too. There are difficulties in doing so!
however. A combination of software and hardware must be used to do the Dob.A &ate+ay connects networks of different kinds! like connecting a network of #Cs to amain frame network. This can be comple56
A 'rid&e connects networks of the same type. This Dob is simple.
A router connects several networks. A router is smart enough to pick the right path forcommunications traffic. 1f there is a partial failure of the network! a router looks for analternate route.
Suppose the accounting! advertising! and shipping departments of a company each havenetworks of #Cs. These departments need to communicate with each other! but onlysometimes. 1t would be easier and cheaper to connect them to each other than to put themall on the same larger network. The best arrangement would be for the departmentalnetworks to be of the same kind so that a bridge could be used.
#roblem: Eou need a list of customers who have outstanding balances with your
company of over 8>>>.
1f you are on a network! what happens ne5t when you re3uest data depends on the setupof the host computer! the ser)er. A server is faster and more powerful than the computersconnected to it on the network.
Co!puter to Co!puter
&i!e %er)er
4hen you ask for customers with outstanding balances of over 8>>>! a computer set up
as a file ser)er will send out a copy of the whole Customers file to your computer. Eourcomputer does the search through the file for the customers that meet the criteria of,Balance W 8>>>,.
This is fine unless the Customers file is large. Then it would take a long time Dust to
download the file to your computer. 1t would also take a long time to search through sucha large file.
Click on the image below to see how this works# Click again to stop theanimation#
C!ient %er)er
4hen you ask for the customers with balances of over 8>>>! a computer set up as a
client ser)er does the search itself and sends only the results to your computer.
This is best when the file is large or changes rapidly. 1t takes advantage of the e5tra power of the server and avoids the ,dead time, of a long download.
Click on the image below to see how this works# Click again to stop the
animation#
Quiz on Lesson 1: Communication)or each 3uestion! click on the radio button for your answer. Eou will be notifiedimmediately whether your choice is correct or not. Doubling clicking may work better
Between the hardware and the application software lies the
operatin& syste!. The operating system is a program thatconducts the communication between the various pieces of
hardware like the video card! sound card! printer! themotherboard and the applications.
What can a co!puter do +ithout an operatin& syste!A
Not much66 0etFs look at what happens when you turn on your computer! before theoperating system is involved.
The first screen you see when you turn your computer on will be about the BIO$ +Basic
Input8Output $yste!- of your computer. The B12S is a set of instructions on a ROM chip +Read-Only Me!ory- that controls how the hardware and the operating systemcommunicate. 1tFs a very limited set of instructions.
Notice the instruction to ,Hit DEL if you want to run Setup.,. 2ther
keys might be used for a different brand of B12S. "onFt do this unless you know whatyou are trying to do. Setup allows you change certain features of your computer at a very basic level! but doing it wrong can keep it from working right or even at all6
An older B12S might not understand your newest! spiffiest piece of hardware. 1n thiscase you would have to get a new motherboard or an updated B12S. A newermotherboard will have a B12S that can be updated using software. 1t re3uires making a
physical change on the inside of your computer! running a special software program! thenresetting the motherboard back the way it was. (his is a task only for the brave andtechnically skilled since you can ruin a motherboard very easily!)
After the B12S has gone through its morning wake<up routine! youFll see on your screensomething about running the O$T +o+er On $elf Test-. This is a set of tests of thehardware. 1f! for e5ample! your keyboard is not plugged in or is broken! you will see amessage about ,$eyboard failure, and the computer will stop where it is in the #2ST.There are tests included for the hard drives! memory! and the buses! too. This is only a3uick check<up though and does not guarantee that everything is perfect.
ThatFs it for what the computer can do without an operating system. 1t can wake up andtwitch a little! but it canFt move or talk yet. 1ts nervous system is not working.
Ne5t the computer looks for some kind of operatin& syste!. 1t will usually be set up tolook in the floppy drive first and then on the hard drive. This way if your hard drive fails!you have a way to get the system working enough to diagnose the problem. &nough ofthe operating system to get started will fit on a @P, floppy disk. This part of the operating
system has various names. 0ernel! master program! supervisor! control program are afew. 1n #Cs using "2S or 4indows the term kernel is used.
4hen the kernel is loaded! the computer looks for three files:
co!!and lan&ua&e interpreter The command language interpreter is the program that turns your keystrokes into allthose 8Fs and >Fs for the processor to swallow. )or "2S and 4indows 7J the program isco!!and*co!.
confi&*sys
)rom the config.sys the computer finds what devices are connected! such as a mouse! C"drive! or scanner. The file tells where to look for the directions! called dri)ers! for usingthese devices.
'ere is an e5ample of a config.sys that might be used with 4indows 7J! withe5planations in blue on the right. The 'lue parts cant 'e in the real file. 4in7J doesnFtre3uire a config.sys unless there are devices that you want to run in "2S mode.
DEVICE=C:\WINDOWS\HIMEM.SYS /eisa
This device manages the high memory. =ery important.DEVICE=C:\WINDOWS\EMM386.EXE NOEMS
This device manages the rest of memory. =ery important.DEVICEHIGH=C:\PIONEER\ATAPICD.SYS /S:3 /D:MSCD!!"
This device operates the C" drive. The '1' part says to load the driver '1' inmemory! so the '1(&( device must be loaded too.
autoexec*'at
This file does optional tasks like loading programs that you want to start every time yourcomputer is turned on. Eou may see a lot of messages on the screen as the various programs are started. This file also tells the computer where to look for files! called thepath. (any programs add their own directories to the path when they are installed. The
path can get too long to function right6'ereFs an e5ample of an autoe5ec.bat that might be used under 4indows 7J! withe5planations on the right in blue. The 'lue parts cant 'e in the real file* 4in7J doesnFtre3uire an autoe5ec.bat but you might want to change some of the defaults or to havesome things to run in "2S mode.
These two lines tell programs where to put temporary files#':\(i)*+(s\'+,,a)*\,s'*e-.e-e /*:ATAPICD.SYS
Starts driver for C"< 2(#ECHO O
Allows some lines to not show onscreen when this file is run#PROMPT 01
Sets how the command line will look#SET PATH=C:\WINDOWS2C:\WINDOWS\COMMAND2C:\2
Tells where to look for files when full name with directories is not givenREM Tis is a 4e,a45.
1f a line starts with &( the computer ignores the rest. So this is a way to write yourselfnotes about what the lines do.
The X in the front of a line keeps that command from displaying on the screen as it ise5ecuted. Some people want to see them A00. (ost of us would rather not think about it6
By the way! if you look on your hard drive under 4indows for these files! you might notsee them. The default installation of some versions of 4indows hides syste! files! whichincludes autoe5ec.bat and config.sys. To view such files you must change a setting. )romany (y Computer or &5plorer window! on the =iew menu! select 2ptions. Then choosethe =iew tab. There is a choice there to show or not show system and hidden files.
DO$ < 4hen your pretty graphical interface breaks! you may have to go to the commandline to fi5 it. &ven within 4indows @.5 and 4in7JH79! it can be faster to type a commandon the un line than to find the right icon to start a program. So! a knowledge of "2Scommands is not yet useless. See "2S Commands
So we see that without the operating system! the computer is paraly%ed. 0etFs look now atthe types and functions of operating systems.
&unctions
All operating systems must handle the same basic tasks. These functions can be divided
The operating system directs the traffic inside the computer! deciding what resource will
be used and for how long.
Ti!eTime in the C#? is divided into ti!e slices which are measured in milliseconds. &achtask the C#? does is assigned a certain number of time slices. 4hen time e5pires!another task gets a turn. The first task must wait until it has another turn. Since timeslices are so small! you usually canFt tell that any sharing is going on. Tasks can beassigned priorities so that high priority +fore&round- tasks get more time slices than low priority +'ac,&round- tasks.Me!ory
(emory must be managed also by the operating system. All those rotating turns of C#?use leave data waiting around in 'uffers. Care must be taken not to lose data66 2ne wayto help out the traffic Dam is to use )irtual !e!ory. This includes disk space as part of
main memory. 4hile it is slower to put data on a hard disk! it increases the amount ofdata that can be held in memory at one time. 4hen the memory chips get full! some ofthe data is pa&ed out to the hard disk. This is called s+appin&. 4indows uses a s+ap file
for this purpose.
Input and output
)low control is also part of the operating systemFs responsibilities.The operating system must manage all re3uests to read datafrom disks or tape and all writes to these and to printers.
To speed up the output to printers! most operating systems now allow for print
spoolin&! where the data to be printed is first put in a file. This frees up the processorfor other work in between the times data is going to the printer. A printer can onlyhandle so much data at a time. 4ithout print spooling youFd have to wait for a print
Dob to finish before you can do anything else. 4ith it you can re3uest several print Dobs
and go on working. The print spool will hold all the orders and process them in turn.
!onitoring sstem activities
$yste! perfor!ance
A user or administrator can check to see whether the computer or network is gettingoverloaded. Changes could be made to the way tasks are allocated or maybe a shoppingtrip is in order6 System performance would include response ti!e + how long it takes forthe computer to respond when data is entered- and CU utili2ation +comparing the timethe C#? is working to the time it is idle.-
$yste! securitySome system security is part of the operating system! though additional software can addmore security functions. )or multiple users who are not all allowed access to everything!there must be a lo&on or lo&in procedure where the user supplies a user ID and a secretpass+ord. An administrator must set up the permissions list of who can have access towhat programs and what data.
(i#e an" Disk !anagement
$ eeping track of what files are where is a maDor Dob. 1f you canFt find a file! it doesnFt
help to know that it is safe and secure somewhere. So an operating system comes with
basic file !ana&e!ent commands. A user needs to be able to create directories forstoring files. (Dumping everything in one pile soon becomes the needle0in0the0haystack story#) A user needs to copy! move! delete! and rename files. This is the category ofoperating system functions that the user actually sees the most.
A more technical task is that of dis, !ana&e!ent. ?nder some operating systems yourhard disk can be divided up! or partitioned into several )irtual dis,s. The operatingsystem treats each virtual disk as though it were a physically separate disk. (anagingseveral physical andHor virtual disks can get pretty comple5! especially if some of thedisks are set up with different operating systems. (ome folks are never satisfied with 1ustone of anything!)
The first allows only one pro&ra! to run at a time. This means that if you are working
in a spreadsheet and want to write a memo! you must shut down the spreadsheet
application and open up a word processor. This is annoying! especially if you need to3uote some data from the spreadsheet in your memo6 So new operating systems weredesigned that allowed !ultiple pro&ra!s to run at the same time.
The simplest form is !ulti-tas,in&. 4hat this really means is that the programs aretaking turns with the processor. 1t allows a single user to have the spreadsheet and the
word processor open at the same time! and even more. Now the user can see tocopy data from one to the other. (uch better66
The computer must decide on how many time slices each program gets. Theactive program gets the most. Ne5t is programs that are doing things but which
arenFt the foreground program. 0ast is programs that are open but arenFt doing anything.They need a little bit of time every now and then to see if they are supposed to dosomething yet.
The ne5t step up in comple5ity is !ultiple users. 2n a network several users can beusing the same computer or even the same program on that computer. This is called ti!e-
sharin&.
1f a computer has !ultiple CUs! it can do !ultiprocessin&. ather than a single C#?giving out turns to various programs! the different C#?s can work simultaneously. Speed
increases immensely. 2f course cost does! too6
1t is possible for a computer to use more than one operating system through the use of)irtual !achines.,=irtual, means itFs not really there. But programs written for differentoperating systems are fooled into thinking their re3uired operating system is present.
2riginally the operating system was created by each company that manufactured a
processor and motherboard. So each operating system was proprietary! that is! uni3ue toeach manufacturer. #roblem: changing to a new computer meant your software had to bereplaced6 Not good marketing. So there was pressure early on to standardi%e things sothat software could be transferred to the new (and of course better!) computer. Thisre3uired more standardi%ation in operating systems.
The winner in the #C market was M$-DO$! (icrosoftFs Dis, Operatin& $yste!! and itstwin at 1B(! #C<"2S! also written by (icrosoft. Now itFs hard to recall those days wheneach computer had its own uni3ue operating system. (ore on "2S Commands
Windo+s and Windo+s ; are actual operating systems on their own. The previousversions of 4indows use "2S as the operating system and adding a graphical userinterface which will do multitasking. But with 4indows 7J (icrosoft released anoperating system that can take advantage of the @<bit processors.
Windo+s Me +4indows (illennium &dition- is an upgrade of 4indows 79! release dateSept. 8;! >>>. The system resources re3uired for this operating system are significantlyhigher than previous versions of 4indows.
Windo+s NT +the NT apparently came from New Technology- is an operating systemfor client<server type networks. The latest version of NT has a user interface that is practically identical to 4indows 7J. Since 4indows NT is designed for the higherdemands of networks! it has higher demands itself for disk space and memory.
Windo+s >::: is an upgrade of 4indows NT rather than of 4indows 79.
Windo+s E is an upgrade to 4indows >>>. 1t comes in two versions < 'ome and#rofessional. The #rofessional version contains all the features of the 'ome version plusmore business features! like networking and security features. (icrosoft: 4hich editionto choose
Windo+s C5 is for small devices like palmtop and handheld computers. 0ite versions ofa number of maDor applications are available to run on these devices. Eou can link yoursmall computer to a regular one to synchroni%e documents and data.
The 3pple Macintosh is a multitasking operating system that was the first graphicalinterface to achieve commercial success. The (ac was an immediate success in the areasof graphics production! and still commands the lionFs share of that market. Apple made amaDor marketing error when they decided to keep their hardware and software undertight control rather than licensing others to produce compatible devices and programs.4hile the Apple products were of high 3uality! they were always more e5pensive than
comparable products that were compatible with (icrosoftFs "2S operating system.AppleFs share of the computer market has dropped to an estimated .;Y worldwide and@.;9Y of the ?S market +(ac4orld /uly @! >> -. This is an e5ample of how a nearlock on a market can be lost in a twinkling.
(ac 2S K! =ersion 8>. +/aguar- is the current version. Since /anuary >>! all new (accomputers use (ac 2S K.
1B(Fs @<bit operating system is O$8>. This is a popular system for businesses withcomple5 computer systems from 1B(. 1t is powerful and has a nice graphical interface.#rograms written for "2S and 4indows can also run on this system. This system hasnever really caught on for #Cs.
UNIE is an operating system developed by Bell 0abs to handle comple5 scientific
applications. ?niversity networks are likely to use ?N1K! as are 1nternet Service#roviders. A lot of people have e5perience with ?N1K from their college work. (anycomputer old<timers love ?N1K and its command line interface. But all those commandsare not easy to remember for newcomers. K<4indows is a graphical interface for ?N1Kthat some think is even easier to work with than 4indows 79.
inux is an operating system similar to ?N1K that is becoming more and more popular.+And it has the cutest logo6-1t is a open<source program created by 0inus Torvalds at the ?niversity of )inland!starting in 8778. Open source means that the underlying computer code is freely
available to everyone. #rogrammers can work directly with the code and add features.They can sell their customi%ed version of 0inu5! as long as the source code is still open toothers. Eou can find more info at the 0inu5 home site.By the way! the word 0inu5 is generally pronounced with a short i and the accent on thefirst syllable! like 01'<nucks. 'ere is a link to an audio file of 0inus Torvalds pronouncing it in &nglish.
2ther operating systems e5ist and new ones may still appear and take over the market position of the popular ones discussed above. Nothing in computers is so sure as change6
(icrosoft! for e5ample! has adopted a schedule for phasing out online support andupdates for its operating systems.http:HHwww.microsoft.comHwindowsHlifecycleconsumer.msp5 )or e5ample! under this schedule! "ec. @8! >>! is the &20 +&nd of 0ife- date for allversions of (S<"2S! 4indows @.5! 4indows 7J! and 4indows [email protected]. There will be nomore security updates and no technical support of any kind from (icrosoft for productsthat have passed their &20 date.
+hich is most popu#ar2
1t depends on who you ask6 There is no one who can accurately report the true usage ofany operating system. =arious companies can report what they sold. 1nternet sites canreport who comes to visit them. But no one can tally the whole world! or even a wholecountry.
%oo&le# The statistics for oogle for 2ct. and Nov. >>@! are shown below. 1t is clearthat 4indows K# leads the list! with 4in79 and 4in>>> ne5t in line. #oor (ac and0inu5 are not being used much by oogle visitors. 'ow well does oogle reflect thegeneral computing public ThatFs the 3uestion! isnFt it6
e&s+or,s*co!# The statistics for this site! Degworks.com! for Nov. >>@! are similar to
oogleFs! but not 3uite the same. 'idden in the 2ther category is I.@Y for 4indows(&. That operating system must be part of the ;Y for oogle. The general trend is thesame for both sites! however. 4indows K# is overtaking all the rest.
Utility ro&ra!s perform tasks related to the maintaining of yourcomputerFs health < hardware or data. Some are included with theoperating system. But someone always thinks they have a better versionfor you to buy. And they are fre3uently right6
$yste! $oft+are
File Mana&e!ent programs make it easier to manage your files. 1n the high days of "2Sit didnFt take much to improve on the te5t<only type<it<all<yourself methods that "2S provided. (any programs were written to help the user find files! create and organi%edirectories! copy! move! and rename files. Some even used the mouse to point and clickto accomplish these tasks. Eou donFt appreciate the vastness of the improvement untilyouFve tried to do these things from the command line. The newer graphical interfacesthat come with operating systems like 4indows 7J have reduced the need for alternatefile management programs.
Dis, Mana&e!ent programs involve formatting and defragmenting disks.Defra&!entin& means putting files on the disk so that the whole file is in se3uence. Thisreduces the time to access the file. Some disk management programs even let you specifythat certain files that are accessed often! like the operating system itself and fre3uentlyused programs! are at the front of the disk. Anything that speeds things up will havecustomers.Me!ory Mana&e!ent software handles where in A( programs put their current data.They move certain memory<resident items out of the way. This can effectively increasethe memory available by getting all the unused pieces together in one spot! making auseable amount.
A Bac,up program! which also restores the backed up data! is a must if you have anydata at all that you want to keep around for a while. The software will compress the datato take up the least space +ecall the problem with slack space we found in the discussionof Storage: "isk )ormat-.
Data Reco)ery programs are for those who Dust said ,4hoops6, They attempt to recover
deleted or damaged +corrupted- files.
Data Co!pression programs s3uee%e out the slack space generated by the formattingschemes! as discussed under Storage: "isk )ormat.
3nti-)irus programs are another must<have program. They monitor the computer for theactivity of viruses! which are nasty little programs that copy themselves to other disks tospread to other computers. =iruses can be merely annoying or they can be vastlydestructive to your files.
Quiz on Lesson 3: Sstem So4t*are
)or each 3uestion! click on the radio button for your answer. Eou will be notifiedimmediately whether your choice is correct or not. Doubling clicking may work better
?se the Back button to return to lesson pages if you want to review any information or goto the 'ome #age.
8. The operating system for a computer does the following:
&5ternal devices connect to the computer in the back. The diagram on the left shows the
most common connections. But the arrangement of these is 3uite varied from machine tomachine. The name<brand computers often have uni3ue designs with special connectors
for the peripherals that are sold with the computer.
Connectors come in two types: male and female. The male has pins while the female hasholes.
(ale )emale
On the Inside
4hile you may not often tinker with the insides of your computer! it is a good idea to
know a little about what it is like in there. The diagram at the left shows a basicarrangement.+This tower case is taller than normal and has wide feet for balance.-
The first task is to remove the case so we can see whatFs inside.
Then you can click on the inside parts for a description! which will show up right here.
7. Before printing! you can change the page margins using the dialog bo5.
#rint
)ormat #age
#age Setup
=iew #references
8>. 1f your document (yeport.doc is saved in folder (y"ocswhich is on drive & on your #C! the path to the document is .
&:[(y"ocs.(yeport.doc
&:H(y"ocsH(yeport.doc
&:[(y"ocs[(yeport.doc
Eou have carefully considered what tasks you want your computer system to handle and
what software youFll need for these tasks. EouFve thought about the total cost of computerownership and have a good idea of what you can spend on the computer system itself. Now you are ready to decide on what hardware to buy.
There are entirely too many things to consider when buying a computer system. So youwonFt forget something important! make a list of all the things you re3uire of your newsystem and set priorities. +4e can rarely afford all we want or even need6- ?se one colorfor characteristics that are absolutely re3uired and a different one for things that are Dusthighly desirable.
Not knowing what you actually need your computer to do! 1 can only make my &est
2uess. Below is a table of my current recommendations for purchasing a #C for homeuse! for what itFs worth. +1 donFt have much e5perience with Apple products! so 1 canFt Dudge how useful this list might be for purchasing a (ac.- ?se this to evaluate acomputer system package. Eou can get some real bargains if your needs can be satisfiedwith a system that meets Dust the minimums.
#lease remember that these recommendations may not suit your circumstances well at all.(ost home computers are used for word processing! games! and accessing the 1nternet.ames stretch the capacity of a computer more than anything else6 So keeping well inmind what you e%pect to use your computer for! choose a system and components thatshould be much! much more than necessary. 1n a year or so you will probably find thatyou need all the capacity youFve got and are wishing for more.
"onFt forget the other considerations! like availability and cost of replacement parts andrepair arrangements. A great price for a system that meets your criteria perfectly wonFtmake you happy if you canFt get something fi5ed or replaced.
1n some browsers you can print Dust the table: drag through the table to select it all andthen in the #rint dialog choose #rint selection.
&est 'uess (ecoendations )Hoe *se+ - ,an$ ../
rocessorbare minimum3 #entium 11! or e3uivalent from Cyri5 or A("better3#entium @best G #entium ;Cloc, speed
minimum 3 J>> ('% +('% G megahert%-better3 I>> ('% great3 8 '% +'% G gigahert% G 8>>> ('%-R3M 6!e!ory7
absolute minimum3 ; (Bbetter3 89 (B
great3 456 (B +(B G megabytes-$lots G Bays
minimum3 @ open slots and 8 open bay"ard dis, si2e
minimum3 > Bbetter3 ;> B great3 8> B +B G gigabytesG 8>>> megabytes-Monitor si2e
minimum3 8J,better3 8I, great3 87,! if you have the room on the desk6 #rice is really down. 2r think about a flat panel monitor< prices are falling rapidly(ideo card
minimum3 local bus card with its own cache with ; (B of =A(better3 #C1 card with 9 (B +re3uires a #entium motherboard- great3 @" card A @" card is needed for the new games. Some @" cards must work witha " card. Newer @" cards have @ (B of memory onboard6Operatin& $yste!
4inK#! pre<installed! C" installation disk provided. Be aware that old software may notrun on new operating systems.
1 do not recommend 4indows (e at all.4in79 is good! but (icrosoft is stopping its phone support of 4in79 on /an. 8! >>;.2n /an. 8@ (icrosoft announced an e5tension but they only promise to ,review, security
updates.
,(icrosoft will also continue to offer a variety of self<help resources on the #roduct Support Services 4ebsite until at least /anuary 8! >>! two years after phone support for 4indows 79 ends on /anuary 8!>>;.,- http:HHsupport.microsoft.comHdefault.asp5prGw79
$oft+are
minimum3 anti<virus! word processingbetter3 maDor anti<virus program! an office suite like (icrosoft 2ffice or 0otusSmartSuite that includes word processing! spreadsheet! database! etcbest3 pre<loaded with the system < the software you need specifically
+Be aware that low end computers may come with (icrosoft 4orks installed! which isnot the same as (icrosoft 2ffice.-
CD-ROM
minimum3 ;9K speed +canFt buy a slower one new6-better3 These are getting faster than 1 can keep up with6
consider3 C"<4 with read speed at least ;K.
$ound card
Sound Blaster or compatibleU may be part of C"<2( package along with speakers
rinter
minimum3 ink Det or bubble Det! at least pages per minute!+consider color though it is slower-
better3 black and white laser for best print 3uality.best GColor laser< #rices are now under 8>>>6 but toner is e5pensive
minimum3 surge protection strip or console with phone Dackbetter3 ?#S with phone Dack and J < 8> minute backup powerbest3 includes software to auto<close and shut downMode!
minimum3 J. $bps speed
better3 1S"N! or A"S0 +also called Dust "S0-best3 cable modem! as it becomes available
Where to /uy?
2ne maDor consideration about what computer system to buy is 4here to buy it. There
are a number of sources! each with their own Advantages and "isadvantages.
Chain co!puter store
Advantages:$nowledgeable staff can advise you&asy to e5changeepair what they sell0arge stock on hand#rices usually 2$. National brands'elp with installationHconfiguration problems close at hand
Disadvantages:epair shops vary in 3ualityStaff may not be well<trained if turnover is high'igh minimum charge to work on your computer(ay charge for any configuration assistance1mpersonal
$!all co!puter shop
Advantages:$nowledgeable about their own stock(ore personal(ore fle5ible about pricingClones < computers put together from off<the<shelf parts! making replacement parts and
repairs easier.'elp with installationHconfiguration close at hand
Disadvantages:0ittle stock on hand. (ust order.
#ricing tends to be somewhat higherDirect
Advantages:#rices may be lowerCan order non<standard components4arranty comes from manufacturer and not store
Disadvantages:(ust order and wait&5changes for broken parts difficult'arder to get help for installationHconfiguration problems#arts may be more e5pensive than for a clone.
Catalo&
Advantages:0ower prices6(ost accept returns for any reason
Disadvantages:(ust order and wait.(ust ship to return broken or unsatisfactory order No assistance for installationHconfiguration
So what conclusions can we draw about where to buy a system
8. 4hen co!parin& prices! be sure you are not comparing apples to oranges.. Consider possi'le expenses like shipping returns and technical assistance.
@a. 1f you are ,no+led&ea'le about what you want and can tolerate the shippin& +aits!order from a catalo& for the best price. ?se a local co!puter shop to put together Dustthe right system from components.
@b. 1f you are ne+ to co!puters! buy from a store where you can &et assistance andadvice and can return unsatisfactory merchandise. A helpful! local shop is more importantthan a somewhat lower price.
Quiz on Lesson 9: On 7our O*n
8. Eou can count on prices for computer<related products to .
rise faster than inflation.
stabili%e to a consistent price now that the market is mature.
fall as newer! more advanced versions are released.
be totally unpredictable.
. 4hich are e5amples of the hidden costs of owning a computera. operating system b. printer paper
c. printer tonerd. mousee. tape for backups
abcde
bcde
bce
e
@. The kind of software which you can try out before buying butwhich has maDor functions disabled is .
save! until you are sure everything is working right
save for about months
trash it since you wonFt need it again
8>. A program which is an ,upgrade version, .
merely adds features to an e5isting program
re3uires the presence of a previous version of the program to install
is a Dust a new version of a program
is a more advanced high<end type program
Computers are showing up everywhere you look! and even in places you canFt see.
Computers check out your groceries! pump your gas! dispense money at the AT(! turn
the heat on and off! control the way your car runs. TheyFre everywhere6 TheyFreeverywhere6
1n fact! the computer is rapidly becoming! if it hasnFt already gotten there! as tightlywoven into the fabric of our lives as the automobile. The analogy runs 3uite deep.
Co!puter Types
4hen automobiles were new! many people said ,Those smelly! loud! complicated thingswill never replace the horse6, And ,Those things break down in Dust a few miles! while
my faithful horse goes on and on and repairs itself6, Nowadays itFs hard to imagine theworld without all the variety of four<wheeled! internal combustion vehicles. 'ow manycan you name Sedans! pickup trucks! fire engines! front<end loaders! ;<wheelers! golfcarts! bulldo%ers! cranes! vans! dump trucks... 4e have an ,automobile, for every purposeunder heaven < and in different models and colors! too.
So it is with computers. There are different kinds of computers for different purposes.They are Dust as varied in si%e! e5pense! and ability as our more familiar ;<wheeledvehicles are.
Consider this set of lessons ,Beginning "riverFs &d, for the computer. 4hat might becovered in a "riverFs &ducation course in high school 'ow the engine works. #arts of
the car. 'ow to turn it on. 'ow to shift gears. ules of the road. 0aws. #roper signaling.0ane changing. Basic maintenance. Changing a flat. )illing up with gas. Some clues onwhen ,EouFd better stop the car now6,
The topics covered here will introduce you to a similar set of topics about computers.4hen you finish! youFll be Dust as prepared to ,drive, a computer! as you were to drive acar when you finished "riverFs &d. Scary thought! isnFt it That clearly means you willneed lots of practice with a skilled ,driver, in the passengerFs seat before you can beconsidered ,safe on the road6, But we can get you started6 But! really! youFll understandthe basic ideas behind computers! some of the ills that affect computers! and some of the basic safety measures to take to keep your computer healthy. EouFll gain some
knowledge of how we got to todayFs computers and what lies ahead. 1tFll be great6 So letFsget started....
What is a computer?
A comp!ter is an electronic de"ice t#at e$ec!tes t#einstr!ctions in a program A comp!ter #as %o!r %!nctions&
Computers for personal use come in all shapes and si%es! from tiny D3s +personal
digital assistant- to hefty C +personal computer- towers. (ore speciali%ed models areannounced each week < trip planners! e5pense account pads! language translators...
4hen talking about #C computers! most people probably think of the des,top type!which are designed to sit on your desk. +Bet you figured that one out6- The to+er and thesmaller mini<tower style cases have become popular as people started needing more roomfor e5tra drives inside. epairmen certainly appreciate the roominess inside for all thecables and circuit boards ... and their knuckles.
A +or,station is part of a computer network and generally would be e5pected to havemore than a regular desktop #C of most everything! like memory! storage space! andspeed.
The market for the smallest #Cs is e5panding rapidly. Software is becoming available forthe small types of #C like the pal!top +C- and handheld +"C-. This new softwareis based on new operating systems like 4indows C& +for Consumer &lectronics-. Eoumay find simplified versions of the maDor applications you use. 2ne big advantage for thenewer programs is the ability to link the small computers to your home or work computerand coordinate the data. So you can carry a tiny computer like a #alm#ilot around toenter new phone numbers and appointments and those great ideas you Dust had. Then lateryou can move this information to your main computer.
4ith a Ta'let C you use an electronic stylus to write on the screen! Dust like with a penand paper! only your words are in di&ital in, . The Tablet #C saves your work Dust like
your wrote it +as a picture-! or you can let the 'and ecognition +'- software turn yourchicken<scratches into regular te5t.
computers or terminals which allows hundreds of people to work at the same time on thesame data. 1t re3uires a special environment < cold and dry.
%upercomputers
The superco!puter is the top of the heap in power and e5pense. These are used for Dobs
that take massive amounts of calculating! like weather forecasting! engineering designand testing! serious decryption! economic forecasting! etc.
A list of the top J>> supercomputers <who made them! where they are installed andwhat they are used for.
A allery of images of Cray supercomputers < from the current model back to theearliest.
The &irst )ray supercomputer %as intro!uce! in 9:;< " the )ray"9 4
'istri"uted or 1rid Computing
The power needed for some calculations is more than even a single supercomputer can
manage. 1n distri'uted co!putin& using a C &rid many computers of all si%es canwork on parts of the problem and their results are pooled. A number of current proDectsrely on volunteers with computers connected to the 1nternet. The computers do the work
when they are not busy otherwise.
The proDects that need distributed computing are hi&hly technical. )or e5ample! theS&T1X'ome proDect looks for signs of intelligent communication in radio signalscoming from space. (8- stands for earch for 89tra0errestrial -ntelligence#)
1f you volunteer your computer for this proDect! you might be asked to load a smallscreen<saver program onto your own computer. 4hen the computer is not busy! the
screen saver comes on. The program downloads some signal data! starts to analy%e it! andlater reports the results back to S&T1X'ome. 2nce the program is installed! you do nothave to do anything else but watch the progress in the screen saver.
Another method does not use a screen saver! but uses any idle time on your computer to
work on the proDect. esults are sent to the proDectFs home over the 1nternet.
Some current distributed computing efforts are:
&ntropia: )ightingA1"SX'omemodeling evolution of resistance to drugs and designing better A1"S treatments)oldingXhomeworking on how proteins fold! which is important to understanding how they work andreproduce"istributed.Net
cryptography and mathematical problems20&(X'ome completed: evolving robots +enetically 2rgani%ed 0ifelike &lectro (echanics-#i'e5 calculating the value of #i to certain large places +done6-
Other Important Terms
Server
The term ser)er actually refers to a computerFs functionrather than to a specific kind of computer. A server runs anetwork of computers. 1t handles the sharing of e3uipmentlike printers and the communication between computers onthe network. )or such tasks a computer would need to besomewhat more capable than a desktop computer. 1t wouldneed:
The !inico!puter has become less important since the #C has gotten so powerful on its
own. 1n fact! the ordinary new #C is much more powerful than minicomputers used to be.2riginally this si%e was developed to handle specific tasks! like engineering and CA"
calculations! that tended to tie up the main frame.
)or more on the history of computing: The Computer (useum 'istory Center Thecenter traces the development of the computer. The site includes a timeline that is sorted by year or by topic. Eou can also search for information on people! companies! and products in the computer industry.
Quiz on Lessons 9:
Overvie* $pp#ications)or each 3uestion! click on the radio button for your answer. Eou will be notifiedimmediately whether your choice is correct or not. Doubling clicking may work better
?se the Back button to return to lesson pages if you want to review any information or goto the 'ome #age.
8. The software application that is used the most often is .
word processing
desktop publishing
spreadsheet
database
graphical presentation
. The largest! fastest! most e5pensive type of computer is the .
@. A computer which links several #Cs together in a network iscalled a .
minicomputer
server
client
main frame
;. To publish a maga%ine a application would be best.
word processing
desktop publishing
spreadsheet
presentation graphics
J. /ulian is a sales rep calling on up to > businesses a week. Tokeep track of his appointments and his clientsF addresses and phonenumbers! he should use a .
ro&ra!s are the sets of instructions that direct the computer.
Co!!ands are special codes or ,ey +ords that the user inputs to perform a task! like?N ,ACC2?NTS,. These can be selected from a menu of commands like ,2pen, onthe )ile menu. They may also be chosen by clicking on a co!!and 'utton.
User response is the userFs answer to the computerFs 3uestion! such as choosing 2$!E&S! or N2 or by typing in te5t! for e5ample the name of a file.
The first input de)ice we will look at is the 0ey'oard. The image used on the ne5t pageto illustrate the various keys may not look like the keyboard you are using. Severalvariations are popular and special designs are used in some companies. The keyboards
shown below put the function keys in different places. The &nter and Backspace keys aredifferent shapes and si%es. 2ne has arrow keys while the other doesnFt. 1tFs enough toconfuse a personFs fingers66
The backslash key has at least @ popular placements: at the end of the numbers row!above the &nter key! and beside the &nter key. 4e also have the new 4indowskeyboards which have two new keys. 2ne pops up the Start (enu and the other displaysthe right<click conte5t sensitive menu. &rgonomic keyboards even have a different shape!curved to fit the natural fall of the wrists.
A variety of pointing devices are used to move the cursor on the screen.
The most commonly used ones have two or three buttons to click for special functions.
Mo!se
A ball underneath rolls as the mouse moves across the mouse pad. The cursor on thescreen follows the motion of the mouse. Buttons on the mouse can be clicked or double<clicked to perform tasks! like to select an icon on the screen or to open the selecteddocument.
There are new mice that donFt have a ball. They use a laser to sense the motion of themouse instead. 'igh tech6
ractice clicking on the images of mice to the right. The image will change with asuccessful click.
Advantage:(oves cursor around the screen faster than using keystrokes. Disadvantage:e3uires moving hand from keyboard to mouse and back.epeated motion can lead to carpal tunnel syndrome
Track'all1nstead of moving the whole mouse around! the user rolls the trackball only! which is onthe top or side.
"oes not need as much desk space as a mouse.1s not as tiring since less motion is needed. Disadvantage:e3uires fine control of the ball with Dust one finger or thumb.epeated motions of the same muscles is tiring and can cause carpal tunnel syndrome.
Glidepad?ses a touch sensitive pad for controlling cursor. The user slides finger across the padand the cursor follows the finger movement. )or clicking there are buttons! or you can tapon the pad with a finger. The glidepad is a popular alternate pointing device for laptops.
Advantage:"oes not need as much desk space as a mouse.Can readily be built into the keyboard.'as finer resolution. That is! to achieve the same cursor movement onscreen takes lessmovement of the finger on the glidepad than it does mouse movement.Can use either buttons or taps of the pad for clicking. Disadvantage:The hand tires faster than with a mouse since there is no support.Some people donFt find the motion as natural as a mouse.
Game De"icesCursor motion controlled by vertical stick +Doystick- or arrow buttons +gamepad-
Advantage:A Doystick gives a more natural<feeling control for motion in games! especially those
where you are flying a plane or spaceship.Both have more buttons for special functions than a mouse and can combine buttons foreven more actions. Disadvantage:(ore e5pensiveBulkyBetter ones re3uire an additional peripheral card for best performance
)en *np!t?sed esp. in #ersonal "igital Assistants +#"A-#en 1nput is used for:
"ata 1nput < by writing. #"A recogni%es your handwriting. (-f only your friends could$ too!)#ointing "evice <)unctions like a mouse in moving a cursor around the screen and clicking by tapping thescreen.Command estures <
Eou can issue commands by moving pen in patterns. So a certain kind of swirl wouldmean to save the file and a different kind of swirl could mean to open a new file.
Advantage:Can use handwriting instead of typingCan use gestures instead of typing commandssmall si%e Disadvantage:(ust train device to recogni%e handwriting.(ust learn gestures or train device to recogni%e the ones you create
Can lose the pen which is not usually attached to the device
To!c#screen(ake selection by Dust touching the screen.
Advantage:1tFs natural to do < reach out and touch something. Disadvantage:1tFs tiring if many choices must be made.1t takes a lot of screen space for each choice since fingers are bigger than cursors.
Converts drawings! photos! etc. to digital signal.The tablets have special commands
Advantage:"onFt have to redraw graphics already created Disadvantage:&5pensive
A ter!inal consists of a keyboard and a screen so it can be considered an input device!
especially some of the speciali%ed types.
Some come as single units.
Terminals are also called:
• Display Terminals • ideo Display Terminals or DT
A du!' ter!inal has no ability to process or store data.
1t is linked to minicomputer! mainframe! or supercomputer. The keyboard and viewing screen may bea single piece of e3uipment.
An intelli&ent4 s!art4 or pro&ra!!a'le ter!inal can process or store on its own! at
least to a limited e5tent. #Cs can be used as smart terminals.
A point-of-sale ter!inal +O$- is an e5ample of a special purpose terminal. These havereplaced the old cash registers in nearly all retail stores. They can update inventory whilecalculating the sale. They often have special purpose keys.)or e5ample! (c"onalds has separate touchpads for each food item available.
Multi!edia is a combination of sound and images with te5t and
graphics. This would include movies! animations! music! people talking!sound effects like the roar of a crowd and smashing glass.
So!nd *np!t
ecording sounds for your computer re3uires special e3uipment.
(icrophones can capture sounds from the air which is good forsound effects or voices. )or music the best results come fromusing a musical instrument that is connected directly to thecomputer. Software can combine music recorded at different
times. Eou could be a music group all by yourself <singing and playing all the parts6
Voice *np!t
=oice input systems are now becoming available at the local
retail level. Eou must be careful to get the right system or youFll be very disappointed.
"ecide first what you want to do since a voice input program maynot do all of these:
"ata entry < Talking data into the computer whenyour hands and eyes are busy shouldcertainly be more efficient. EouFdhave to be very careful about your pronunciation6
Command and control < Telling the computer what to doinstead of typing commands! likesaying ,Save file,. Be careful here!
too. The dictionary of understoodwords does not include some of themore ,forceful, ones.
Speaker recognition < Security measures can re3uire you tospeak a special phrase. The computermust recogni%e your voice to let youin.
Speech to te5t < Translating spoken words direct totype would suit some authors Dustfine. EouFd have to watch out forthose ,difficult to translate, phraseslike ,hmmm, and ,ah! well! ...ummm.,
+Nov. >>>- < Speech recognition and speech<to<te5t software isgetting better rapidly. At least one retail version has the training period down to J minutes and ignores those filler phrases like,ummm,. This is getting e5citing and actually useful6
A number of companies are now using speech recognition in theirtelephone systems. )or e5ample to find out what your bankaccount balance is! instead of punching in your account number onthe phone keypad and choosing option @ for current balance! youcould speak your account number and say ,Current balance,. Thecomputer will even talk back and tell you what it thinks you saidso you can make corrections. 4ow6
,ow do t#ey c#ange "oice to data8. Con)ert voice sound waves to
Types of (oice Reco&nition syste!sS0ea5e4*e0e)*e)s7se,
The software must be trained torecogni%e each word by each individualuser. This might take hours of talkingthe dictionary into the computer! to beoptimistic.
S0ea5e4i)*e0e)*e)s7se,
The software recogni%es words frommost speakers with no training. 1t usestemplates. A strong accent would defeatthe system! however.
Dis'4ee s0ee'4e'+1)ii+)
The speaker must pause between wordsfor the computer to tell when a wordstops.
,'ow soon can we ship a do%en of product RJ in blue to Nashville, < andget an answer66
Science fiction has come to life666
Video *np!t
A di&ital ca!era takes still
photos but records the pictureson computer disks or memory
chips. The informationcontained can be uploaded to acomputer for viewing.
A )ideo ca!era or recorder
+=C- can record data that can be uploaded to the computerwith the right hardware.Though it is not digital data!you can still get good resultswith the right software.
Both of these take huge amounts of storage. #hotosmake for very large files.
Huic,Ca! by Connecti5 is a
newcomer to the video world. 1tis a tiny video camera designedespecially to sit on yourcomputer. 1t feeds picturesdirectly to the computer < notape or film to develop. 2fcourse you are limited by thelength of the cable that connects
the camera to the computer. Butlike any camera! it will take a picture of what you point it at6
So what do people do withuickCam They use it forvideo conferencing over the
1nternet. They show the worldwhatFs going on outside theirwindow +weather! traffic-. Theytake digital pictures and makemovies< family! pets! snowstorms! birthday parties!whatever.
The first goal of data auto!ation is to a)oid !ista,es in data entry by
making the initial entering of the data as automatic as possible. "ifferentsituations re3uire different methods and e3uipment.
A second goal of data automation is to a)oid ha)in& to re-enter data to perform a different task with it.
)or e5ample! the old style cash register would add up your purchase and calculate theta5. The clerk entered the amounts by hand +the data entry part-. 0ater the numbersoff the store copy of the cash register tapes would have to be added up manually! orentered into a computer program +another data entry task-. )or an up<to<dateinventory someone would have to go count all the things on the shelves +a third dataentry task-.
4ith modern data automation! using bar codes on every item in the store! a computercheck<out register along with a bar code scanner will calculate the sale plus transferthe information directly to the computer that does the store bookkeeping plus adDustthe inventory records by subtracting the items Dust sold. The human errors possible ateach step of data entry are now avoided. 2f course! there are still ways for errors tooccur! Dust not as many. 1n addition! a new feature is available with computeri%edcash registers < a receipt that states the name of the item bought as well as the price.
1enera! 'e)ices
)age
scanner-
The scanner works like a copy machine. 1t captures a whole page and converts it to digital image. 1t cannot be edited atthis point.
,and
scanner-
Eou move the device across the document or picture. 1t willcapture only a section of a page or a large image. So the pieces of anything wider than the scanner would have to berecombined with some nifty software.
%pecia! types of characters read with specia! de)ices
.ar Codes- etail shops now use printed barcodes on products to track inventoryand calculate the sale at the checkoutcounter. The ?S #ost 2ffice uses barcodes to sort mail! but the bars are
different from those used for pricing products.
Optical
Marks-
e5ample < test scoring
A special machine ,reads, the marks.4oe to the student who takes a test withthis kind of score sheet and doesnFt getthose bubbles colored in correctly6
Bank account R is printed in special inkwith magnetic3ualities which can beread by the rightmachine.
OpticalC#aracters-
There are coding systems that use lettersor special characters that are especiallyshaped to be easy for machines to read.
OC0 software
O ptical Character R ecognition: This software takes a scanned image and converts thecharacters in the image into computer characters. The document can now be editedwith a word processor. This is a very tricky process. "ocuments must be carefullychecked for wrong conversions. 1f the original print was not very crisp and clean!errors are very likely. (anually checking for proper translation is necessary. These programs are getting really good if they have a clear scan to work with.
A famous slogan in computing sums up the importance of accurate data:
%I%O %ar'a&e In4 %ar'a&e Out
Conclusions are no better than the data they are based on.
A maDor task for any program that accepts data is to try to guarantee the accuracy of
the input. Some kinds of errors cannot be caught but many of the most common kinds
of mistakes can be spotted by a well<designed program.
A program should attempt to do the following:
8. test data type and for!at e5. HaH7 is not a date
e5. 1f a phone number should have e5actly 8> digitswith the area code! then JJJ<8@ is notacceptable.
. test data reasona'leness e5. @8 should not be a personFs age
e5. A sale of J>!>>> worth of chewing gum at thecorner market is probably missing a decimal pointsomewhere6
@. test data consistency e5. A manFs death date should be later than his birthdate6
e5. The sum of the monthly paychecks should be thesame as the total pay for the year.
;. test for transcription andtransposition errors
e5. Typing IJJ; instead of I<J; is a transcriptionerror! typing the wrong character.
e5. Typing II9 instead of II9 is a transpositionerror! interchanging two correct characters.
Both are very hard to check for.
Quiz on Lesson ;: Input)or each 3uestion! click on the radio button for your answer. Eou will be notifiedimmediately whether your choice is correct or not. Doubling clicking may work better
?se the Back button to return to lesson pages if you want to review any information or goto the 'ome #age.
rocessin& is the thin,in& that the computer does < the calculations! comparisons! and
decisions. #eople also process data. 4hat you see and hear and touch and feel is input.Then you connect this new input with what you already know! look for how it all fitstogether! and come up with a reaction! your output. ,That stove is hot. 1Fll move my handnow6,
The kind of ,thinking, that computers do is very different from what people do.
(achines have to think the hard way. They do one thing at a time! one step at a time.Comple5 procedures must be broken down into =&E simple steps. Then these steps can be repeated hundreds or thousands or millions of times. All possible choices can be triedand a list kept of what worked and what didnFt.
#eople! on the other hand!are better at recogni%ing patterns than they are atsingle facts and step<by<step procedures. )or e5ample!faces are very comple5structures. But you canidentify hundreds and eventhousands of different faces.A human can easily tell one
face from another! evenwhen the faces belong to strangers. Eou donFt recogni%e (omFs face because youremember than (omFs nose is ; cm long! .J cm wide! and has a freckle on the left side6Eou recogni%e the whole pattern of (omFs face. There are probably a lot of folks withnoses the si%e and shape of (omFs. But no one has her whole face.
But a computer must have a lot of specific facts about a face to recogni%e it. Teachingcomputers to pick (omFs face out of a crowd is one of the hardest things scientists havetried to do yet with computers. But babies do it naturally6
So computers canFt think in the same way that people do. But what they do! they do
e5cellently well and very! very fast.
(odern computers are di&ital! that is! all info is stored as a string of %eros or ones < off
or on. All the thinking in the computer is done by manipulating these digits. The conceptis simple! but working it all out gets complicated.
8 'it G one on or off position
8 'yte G 9 bits
So 8 byte can be one of J possible combinations of > and 8. Numbers written with Dust > and 8! are called 'inary numbers.
&ach 8 is a power of so that the digits in the figure represent the number:
G I
> J
> @
> >
G 89 > @ > 9 ; > >
G 8I
&very command and every input is converted into digital data! a string of >Fs and 8Fs.
or more information on binary numbers$ see &ase Arithmetic#
'igita! Codes
All letters! numbers! and symbols are assigned code values of 8Fs and >Fs. A number of
different digital coding schemes are used by digital devices.
Three common code sets are:
3$CII +used in ?N1K and "2SH4indows<based computers-
5BCDIC +for 1B( System @7> main frames-Unicode +for 4indows NT and recent browsers-
The 3$CII code set uses I bits per character! allowing 89 different characters. This isenough for the alphabet in upper case and lower case! the symbols on a regular &nglish
typewriter! and some combinations reserved for internal use. An e5tended ASC11 code setuses 9 bits per character! which adds another 89 possible characters. This larger code setallows for foreign languages symbols and several graphical symbols.
ASC11 has been superceded by other coding schemes in modern computing. 1t is still usedfor transferring plain te5t data between different programs or computers that use differentcoding schemes.
-f you're curious to see the table of A;-- and 8&;D-; codes$ see ;haracter ;odes#
Unicode uses 8 bits per character! so it takes twice the storage space that ASC11 coding!for e5ample! would take for the same characters. But ?nicode can handle many morecharacters. The goal of ?nicode is to represent every element used in every script forwriting every language on the planet. 4hew6 uite a task6
=ersion @ of ?nicode has ;7!87; characters instead of the wimpy few hundred for ASC11and &BC"1C. All of the current maDor languages in the world can be written with?nicode! including their special punctuation and symbols for math and geometry.
At the <nicode site you can view sections of the <nicode code table# he complete table
is too long to put on one page!
Parity
4ith all these >Fs and 8Fs! it would be easy for the computer to make a mistake6 arity is
a clever way to check for errors that might occur during processing.
1n an e)en parity system an e5tra bit +making a total of 7 bits- is assigned to be on or offso as to make the number of on bits even. So in our e5ample above 8>8>88>> there are ;on bits +the four 8Fs-. So the 7th bit! the parity bit! will be > since we already have an even
number of on bits.
1n an odd parity system the number of on bits would have to be odd. )or our e5amplenumber 8>8>88>>! there are ; on bits +the 8Fs-! so the parity bit is set to on! that is 8! tomake a total of J on bits! an odd number.
1f the number of on bits is wrong! an error has occurred. Eou wonFt know which digit ordigits are wrong! but the computer will at least know that a mistake occurred.
(emory chips that store your data can be parity chips or non<parity chips. (i5ing themtogether can cause odd failures that are hard to track down.
The CU! or Central rocessin& Unit! is the
part of the computer where work gets done. 1n most computers! there is one processingchip.
Eou might wonder why 8>; instead of 8>>> bytes per kilobyte. That is becausecomputers donFt count by tens like people. Computers count by twos and powers of .
8>; is 5 5 5 5 5 5 5 5 5 ! that is times itself ten times. 1tFs a ratherconvenient si%e number (for computers!).
Update# Things are changing faster than 1 can type6 The e5planation above is no longerentirely true +/uly >>>-. "ifferent scientific and technical areas are using the wordsdifferently. )or data storage devices and telecommunications a megabyte is 8 >>> >>> bytes. )or data transmission in 0ANs a megabyte is 8 >;9 JI bytes as described above.But for data storage on a floppy disk a megabyte is 8 >; >>> bytes6
4e all are impatient and want our computer to work as fast as possible! and certainly
faster than the guyFs at the ne5t desk6
(any different factors determine how fast your computer gets things done. rocessorspeed is one factor. But what determines the processorFs speed
rocessin&
Processor %peed affected "y:
$yste! cloc, rate G rate of an electronic pulse used to synchroni%e processing
+2nly one action can take place between pulses.-(easured in !e&ahert2 +M"2- where 8 ('% G 8 million cycles per secondThis is what they are talking about if they say a computer is a I>> ('% machine. 1tFsclock rate is I>> million cycles per second.
Bigger number G faster processing
Bus +idth G the amount of data the C#? can trans!it at a time to main memory and to
input and output devices.+Any path bits travel is a 'us.-An 9<bit bus moves 9 bits of data at a time.Bus width can be 9! 8! @! ;! or 89 so far.
Think of it as ,'ow many passengers +bits- can fit on the bus at once to go from one partof the computer to another.,
Bigger number G faster transfer of data
Word si2e G a word is the amount of data the C#? can process at one time.An 9<bit processor can manipulate 9 bits at a time.#rocessors can be 9<! 8<! @<! or ;<bit so far.
Bigger the number G faster processing
Eou want a nice match between the word si%e and the bus si%e and the clock. 1t wouldnFt
do any good to have a bus that can deliver data 89 bits at a time! if the C#? can only use
9 bits at a time and has a slow clock speed. A huge line of data would form! waiting toget off the bus6 4hen computers gets clogged like that! bad things can happen to yourdata. 1tFs like people waiting to get in the theater. After a while! some of them may leave66
here are several physical components of a computer that are directly involved in processing. The processor chip itself! the memory devices! and the motherboard are themain ones.
rocessin&
Microprocessor<a single silicon chip containing C#?! A0?! and some memory.The ROM +Read Only Me!ory- cannot be changed by the user and contains theminimum instructions the computer needs to get started! called 'ootin&.There may also be another chip dedicated to calculations.The microprocessor chip is located on a large circuit board called the !ain 'oard or!other'oard.The physical si%e of a computer chip is very small! as the ant below illustrates.
Me!ory De)ices# =acuum tube <oldest type. "idnFt hold up long and generated a lot of heat.Core <
small metal rings. (agnets tip a ring to left or right! which represents on and off.elatively slow.Semiconductor <integrated circuit on a chip. This is what modern computers use for memory. #ictured below is a I<pin S1((.
$peed
(emory speed measures the time it takes to move data in or out of memory. 1t ismeasured differently for different kinds of memory chips:
•
in nanoseconds +ns - for &"2 and )#( +smaller is faster-8 ns G 8 billionth of a second.• in ('% +higher is faster- for S" S"A(! ""! S"A(! and
"A(.
The capacity of a memory chip is measured in !e&a'ytes. Si%es are measured inmegabytes and come in powers of : 8! ;! 9! 8! @! ;! or 89 (B on one memory board. Several such boards can be installed in the computer to increase the amount ofR3M +Rando! 3ccess Me!ory- available as (ain (emory. (otherboards have onlyso many slots for memory so there are limits. Some motherboards re3uire that all slots befilled and that all slots contain the same si%e memory board. 1t can get frustrating as there
are no warning labels about this6
Quiz on Lesson <: Processing
8. The information processing cycle includes the following processes:
