7/27/2019 Virtual Memory_remaining.doc http://slidepdf.com/reader/full/virtual-memoryremainingdoc 1/13 What is Virtual Memory? This is a method of extending the available physical memory on a computer. In a virtual memory system, the operating system creates a pagefile, or swapfile, and divides memory into units called pages. Recently referenced pages are located in physical memory, or RAM. If a page of memory is not referenced for a while, it is written to the pagefile. This is called "swapping" or "paging out" memory. If that piece of memory is then later referenced by a program, the operating system reads the memory page bac from the pagefile into physical memory, also called "swapping" or "paging in" memory. The total amount of memory that is available to programs is the amount of physical memory in the computer in addition to the si!e of the pagefile. There are several signs indicating it may be time to upgrade your memory. If you see your mouse pointer turn into an hourglass for significant periods of time, if you hear your hard drive woring, or if your computer seems to wor more slowly than you expect, the reason is probably insufficient memory. hen physical memory is insufficient, the system uses #ard $is %pace as memory. This is called "&irtual Memory". %ince access time of 'hysical memory is in tens of (ano%econds and Access time of #ard $is is in Milli%econds, the system slows down considerably. Virtual Memory **DISK BASED MEMORY** • The computer's ability to use disk storage to simulate RAM. The computer uses space on the hard drive as an extension of RAM. It allow computers to run large programs that do not have enough real memory and to also run more than one program at a time. Disadvantages: reduced performance and any data in virtual memory becomes inaccessible if the power goes off. Modems What is a Modem? The piece of e)uipment that allows a computer to communicate with other computers over telephone lines is called a modem. The modem allows the individual to access information from all overthe world and use that information in everyday life. *onnecting with bans, Automatic Teller Machines, cash registers to read credit cards, access travel agents, buy products, e+ mail,access databases, and teleconferencing, the modems provides easy access to many services. iles can be transferred easily, by uploading to another machine, or downloading to your own machine within a matter of minutes. The computer modem can be used as a telephone answering system, and documents can be faxed from one computer to another assuring fast and easy access to important documents. Often 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 digital computer. Such a device is the modem, which comes from Modulate/Demodulate, which is what a modem does. It modulates a digital signal from the computer into an analog one to send data out over the phone line. Then for an incoming signal it demodulates the analog signal into a digital one.
This is a method of extending the available physical memory on a computer. In a virtual memorysystem, the operating system creates a pagefile, or swapfile, and divides memory into units calledpages. Recently referenced pages are located in physical memory, or RAM. If a page of memoryis not referenced for a while, it is written to the pagefile. This is called "swapping" or "paging out"
memory. If that piece of memory is then later referenced by a program, the operating systemreads the memory page bac from the pagefile into physical memory, also called "swapping" or"paging in" memory. The total amount of memory that is available to programs is the amount ofphysical memory in the computer in addition to the si!e of the pagefile.
There are several signs indicating it may be time to upgrade your memory. If you see your mousepointer turn into an hourglass for significant periods of time, if you hear your hard drive woring,or if your computer seems to wor more slowly than you expect, the reason is probablyinsufficient memory. hen physical memory is insufficient, the system uses #ard $is %pace asmemory. This is called "&irtual Memory". %ince access time of 'hysical memory is in tens of(ano%econds and Access time of #ard $is is in Milli%econds, the system slows downconsiderably.
Virtual Memory **DISK BASED MEMORY**
• The computer's ability to use disk storage to simulate RAM. The computer uses space on
the hard drive as an extension of RAM. It allow computers to run large programs thatdo not have enough real memory and to also run more than one program at a time.Disadvantages: reduced performance and any data in virtual memory becomesinaccessible if the power goes off.
Modems
What is a Modem?
The piece of e)uipment that allows a computer to communicate with other computers overtelephone lines is called a modem. The modem allows the individual to access information fromall overthe world and use that information in everyday life. *onnecting with bans, AutomaticTeller Machines, cash registers to read credit cards, access travel agents, buy products, e+mail,access databases, and teleconferencing, the modems provides easy access to manyservices. iles can be transferred easily, by uploading to another machine, or downloading toyour own machine within a matter of minutes. The computer modem can be used as a telephoneanswering system, and documents can be faxed from one computer to another assuring fast andeasy access to important documents.
Often 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 digital
computer. Such a device is the modem, which comes from Modulate/Demodulate, whichis what a modem does. It modulates a digital signal from the computer into an analog one
to 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 complex devices. There are entirely too manycommands, protocols, and configuration choices available. Once you get a modem set up
and woring right the first time, you probably won!t have to tiner with it muchafterwards. "urrah##
Transmission Rate
$onfusion abounds when it comes to measuring the transmission rate of a modem.
Throughput is the term for the entire process % how much data is moved during a certain
amount of time. Since the modem is only part of the process of moving data, getting a
faster modem may not speed up your data transfers.
There are two different parts of the data transfer to measure& the digital process and the
analog process.
DigitalThe rate of digital transmission is measured in bits per seo!d 'bps(. $ommon rates forregular modems are )*.* +bps, .- +bps, and - +bps where the + stands for thousand.
$ompletely digital devices 'discussed below( are much faster. aster is better, of course.
)011 bps would send a )1%page single%spaced report in min. (This is SLOW!!)
A!alogThe analog side is measured in baud where 2 baud is one change in the signal per
second. 3ost people use bps and baud as though they were the same. or speeds of )011 bps and under, this is true, but is it not so for the higher speeds where more than one bit is
transmitted per signal change.
Physical types
There are three physical types of modems&
Externalwhich plugs into a serial port on the back of the computer
!an be moved to a different computer easily."oes not take up a slot inside the computer.#ights on front are visible to show what the modem is doing.Disadvantages:Takes up deskspace.Adds more cables to the tangle.
Internalwhere the phone line plugs directly into card through the back of the computer Advantages:$aves deskspace.$aves a cable.Disadvantages:Re%uires an internal peripheral slot. (They get filled up.)Must use software display to see the lights that show what the modem is doing.
Acousticalwhere the telephone handset is placed into the device which is connected to the computer&ld technology( )ot many of these around any more.* Advantages:!an use a phone without having to move the phone wire.Disadvantages:+ulky.!onnection much more prone to static and interference.nly a standard handset will fit.
Digital Modems
A digital modem does not have to convert between analog and digital signals.
Technically it!s not a 4modem4 at all since it is not modulating and demodulating. A
digital modem is faster than an analog modem.
To get the increase in speed you will have to pay extra 'of course#(. 5igital modems aremore expensive and so are digital data lines from the phone company. The phone
company has to install additional e6uipment for some inds of digital modems.
7ormally a digital modem can receive data at a much higher rate than it can send it out.
That wors out fine for most people because they are only sending out a few responsesinstead of whole web pages or data files.
Warning: Once you have used a high speed device, you will be spoiled forever!
'Integrated Services Digital #etwor( % a digital device using a digital phone line. Itactually should be called a termi!al adapter, but the name modem has stuc. An IS57
device is capable of higher rates than an normal modem, -0 +bps for a single line and2)* +bps for a bonded dual line. IS57 adapters cost more than normal modems and also
re6uire special arrangements with the phone company (and more for hem, of course!).iber optic line is best for the highest IS57 transmission rate, but the copper wires used
in most homes and offices will wor also.
"oe: To ge he highes speeds ou of your #S$" modem, you%ll need a high speed #&O(inpu&oupu) card in he compuer o which o connec he modem'
$able modem
"oos up to your cable T8 line and can receive up to 2. 3bps. 9ou must have cable T8
service with a cable company that also provides data service. 9ou will need a specialcable box to which you connect your T8 and your computer. 9ou will be sharing the line
with all of the cable customers hooed 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. Once
cable modems become popular in your neighborhood, your speed will slow down
noticeably. It will probably still be faster than IS57.
ADS%
'Asymmetric Digital Subscriber %ine( % a new technology that allows a single regular
telephone line to serve for normal phone calls and digital data at the same time. AnA5S: modem receives data at rates ranging from *0 +bps to *3bps, depending on the
particular ind of service. ;ven the slowest type is 0 times faster than the best IS57#<esides great speed, A5S: does not re6uire a separate phone line and you are connectedall of the time. 7o more dialing up#
9ou can use a regular phone on the same line and at the same time that you are surfing
the Internet. 7o more busy signals to your friends and relatives# Another plus is that you
can easily hoo up all of the new parts yourself. This saves a :OT of aggravation sinceyou won!t have to wait on the phone company or the cable T8 guy to show up.
• Internal Modem: This device is a circuit board that plugs into one of the expansion slotsof
the computer. Internal modems usually are cheaper than external modems, but whenproblems occur, fixing and troubleshooting the modem can sometimes prove to be )uite
difficult. The telephone line plugs into the modem port in the bac of the computer.• External Modem: This device attaches to the bac of the computer by way of a cable that
plugs into the modem port. It is usually less expensive and very portable. It can be usedwith other computers very easily by unplugging it and plugging it into another computer.-Remember that you need the right modem software on all the computers you wish touse the modem with.
• Fax Modem: This device can be hooed up to your telephone and used to send
information to your computer. /our computer can also send information to a fax machine.Most computer modems are modems with faxing capabilities.
• ISDN Modem: The I%$( modem re)uires a special phone line called an I%$( line. This
modem sends data at a very fast rate. -012. The advantage of this modem is that it isvery fast and is able to transfer data and graphics at an ama!ing speed with very littleinterference. These modems and lines tend to be )uite expensive.
3uestion4 hat is a modem5
Answer4 A modem is a piece of hardware that allows your computer to tal to other devices overa regular phone line.
A modem converts digital signals from your computer into audible tones that can be transmittedover regular analog phone lines. This conversion process is called M6dulation. The modem onthe other end then transfers those same audible tones bac -or $7Modulates into their originaldigital signals.
M6dulation and $7Modulation is where the name M6$7M comes from.
There are basically two different types of modems -internal+inside of the computer and external+outside of the computer. 7ither type of modem wors technically the same way. 6ne computersends the information digitally and then . . .
. . . the modem translates the digital signals into an analog signal. The analog signal is transfersover the phone wires. The modem at the other end translates the analog signal bac into theoriginal digital signal and sends that information to the computer.
There are actually signals going bac and forth from the two computers to verify that all of theinformation is correct. 2ind+of+lie repeating everything to mae sure that it is all heard correctly.The computers use a system of checsums to repeat the information to save time.
INTERFACE
The type of interface is also important. There are generally only five choices. 'roprietary -lesscommon today, %erial, 'arallel, %*%I, or 8%9..
'roprietary + This is the strangest and most difficult. It could be a mutated version of a serial,I$7, or %*%I controller. These proprietary controllers are usually built into sound cards to control*$ R6M drives, or bundled with tape drives." They have been mostly discontinued since :;;1.
%erial + <enerally your mouse is either on *om: -IR3 = or the '%>? port -IR3 :? and a modemoften over+rides *om? -IR3 @... adding additional *om ports is possible
'arallel + Today motherboards has high speed printer ports -7*' 7nhanced *apabilities 'ort,and 7'' 7nhanced 'arallel 'ort which transfer data faster and better. 'arallel scanners, #arddrives, Tape drives, *$ R6M%, Bip drives, and a few other devices are now feasible to runthrough the printer port without any maCor delays or problems. It is also possible to "chain"multiple devices -up to D in a row off the parallel port.
%*%I + This is a special card in your computer -possibly built+in on very high+end motherboards.There are three "common" types4 :, ?, and @. The advantage of %*%I+: E ? devices is that youcan run up to D devices off 6(7 controller , and it was specifically designed for multi+tasing,networs, and huge files. *ommonly used for high+end scanners and external drives -hard drives,Bip, Fa!, %ysFet, %y3uest, 7xabyte, cd, cdr, cdrw, tape, etc..
%*%I+: is usually Gbit, and has a max speed of 0M9 per second transfer with optimumconfiguration.
%*%I+? is :1 bit minimum, sometimes @? bit &H9 -&esa Hocal 9us or '*I. The %*%I+? cardshave a maximum transfer rate of ?M9 per second, with : to :0M9 average.
%*%I+@ is a little different + is usually @? bit. It is 1G pins, capable of @M9 per second sustainedtransfer '7R $7&I*7, and up to :0 devices on one controller.
8%9 + #ailed as the latest and greatest type of ports available, with up to 1@ devices supposedlybeing able to be daisy chained off each port and speeds in the :?M9 per secondrange and automatic driver installation via firmware.
User Interaces:. The user interface is how the computerJs operating system presents information to the
user and the user gives instructions -commands to the computer.?. There are two inds of 8ser Interfaces
o Text Interface
'resents information to the user in the form of text.
#ave to type in commands or select commands from a menu displayed
as text on the screen. #ard to use or learn, because the user must memori!e and type in
commands.
7xamples4
M%+$os -Micro%oft $is 6perating %ystem
'ro$os -'rofessional $is 6perating %ystem
Many of the Text Interfaces had shells placed over them.
'resents information to the use in the form of pull+down menus andicons.
'ull+down menus the user clics on to display the menu
Icons are small pictures that stand for something, lie a file,volume, trash, or program
The user gives commands to the computer by selecting items from amenu or by clicing on an icon when using a pointing device.
<8Is are easy to learn and use
7xamples4
indows ;G
indows ?
Mac6%
The speed of a printer is measured in,Cps - characters per secondlpm - lines per minuteppm - pages per minute
What print quality? #-#etter -uality as good as best typewriter output)#- )ear #etter -uality nearly as good as best typewriter output"raftused internally or for a test print
The better the %uality the slower the printing.
A more numerical measure of print 6uality is pri!ter resolutio!. 3easured in dots per
i!h 'dpi(, this determines how smooth a diagonal line the printer can produce.
What kind of cable connection? Serial cable $ends data only / bit at a time0rinter can be up to /111 feet away from the computer.
3aximum data transfer speed = 22 ilobits/s '.223bits/s(
Parallel cable$ends data 2 bits at a time0rinter must be within 31 feet of the computer.
3aximum data transfer speed& 22 ilobytes/s '.223<9T;S/s(. This is * times faster
than the maximum serial speed.
7ewer printers may need bi&diretio!al able so that the printer can tal bac to thecomputer. Such a cable is re6uired if the printer can give helpful error messages. It!s
startling, but nice, the first time your computer politely says 4In is getting low4 or4>lease place paper in the AutoSheet feeder.4
Oddly, ?indows @> 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 printer
is processing and printing the document. ?in@> does spool when the printer uses a S<
connection.
USB cable0rinter must be within 3 meters &/4.3 feet* of the computer when connecting straight to thecomputer.56ou can hook up several 3 m. cables and 7$+ hubs in a chain 8 up to 93 meters.:
3aximum data transfer speed& 2) megabits/s '2. 3<9T;S/s( :ots faster#
Best choice:
The new S< 'niversal Serial <us( connection is liely your best choice, if your printer
can use it. It is faster and a S< connector can be unplugged and re%plugged without
turning off the system. S< ports are gradually, but rapidly, replacing parallel ports. The printer cannot handle the data as fast as the S< port can
send it. The real limit on how fast a printer wors is in how
fast printer can get the characters onto the paper.
cylindersThe formatting process sets up a method of assigning addresses to the different areas. It alsosets up an area for keeping the list of addresses. ;ithout formatting there would be no way toknow what data went with what. It would be like a library where the pages were not in booksbut were scattered around on the shelves and tables and floors. 6ou'd have a hard time gettinga book together. A formatting method allows you to efficiently use the space while still being
able to find things.
TracksA track is a circular ring on one side of the disk. <ach track has a number.The diagram shows = tracks.
SectorsA disk sector is a wedge8shape piece of the disk shown in yellow. <ach sector is numbered.n a 3>? disk there are 4 tracks with @ sectors each.n a =? disk there are ! tracks with @ sectors each.
$o a =? disk has twice as many named places on it as a 3>? disk.
A track sector is the area of intersection of a track and a sector shown in yellow.
ClustersA cluster is a set of track sectors ranging from 9 to =9 or more depending on the formattingscheme in use.
The most common formatting scheme for >$s sets the number of trac sectors in acluster based on the capacity of the dis. A 2.) gig hard drive will have clusters twice as
large as a 11 3< hard drive.
' luster is the mi!imum spae used by any read or write. So there is often a lot of sla(
spae, unused space, in the cluster beyond the data stored there.
&ensity Jigher density means more data on shorter tapeMeasured as bpi bits per inch ranges from 211 bpi up to 4931 bpi&o'nloadin$ means to transfer a file to your computer %rom elsewhere.
Uploadin$ means to transfer a file %rom your computer to another.
