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Storage

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Objectives Describe today’s standard floppy disk and

compare it to Zip, SuperDisks, and HiFD disks.

Describe the following kinds of disks: internal hard disks, hard-disk cartridges, and hard-disk packs.

Describe ways to improve hard-disk operations: disk caching, redundant arrays of inexpensive disk, and data compression.

Compare the CD and DVD formats.Describe the different types of optical disks.Describe other kinds of secondary storage:

magnetic tape, Internet drives, and solid state storage.

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Secondary Storage

• Can be used to save information.

• Holds information external from the CPU.

• Allows you to store programs, data, and information permanently.

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Secondary Storage

• Review concepts of temporary storage (RAM) studied in chapter 4:

• RAM (main memory) is temporary or internal storage.

• It has a storage capacity that is usually measured in megabytes.

• If power to the computer is turned off, everything in RAM disappears.

• This type of storage is said to be volatile.

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Secondary Storage• the concepts of permanent storage • Secondary storage is permanent or external

storage.• It has a larger storage capacity and newer

computers may have many gigabytes of storage.

• If power to the computer is turned off, everything on secondary storage remains intact.

• This type of storage is said to be nonvolatile.

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Floppy Disks

• Removable

• Write-protect

• Parts– Tracks– Sectors

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Floppy Disks• Parts of a floppy disk:• Shutter slide – metal component that opens

when disk is inserted into drive (read-write area).

• Write-protect notch – when opened, prevents data from being written to the disk.

• Tracks – closed concentric circles on the disk – invisible to the eye.

• Sectors – wedge-shaped sections on the disk – invisible to the eye.

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Floppy Disks

• Floppy disks are portable, removable storage media.

• They are also known as diskettes, disks, flexible disks, and floppies.

• They are flat circular pieces of Mylar plastic that rotate within a jacket.

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Floppy Disks

• They are used to store programs and data permanently.

• Data is stored as electromagnetic charges on a metal oxide film coating the mylar plastic.

• The presence or absence of the charges (2-state binary code) represents data.

• Data is read from, or written to the disk, through the read-write head in the disk drive.

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Floppy Disks• Today’s standard floppy disk – 1.44 MB 3

½ inch disk.• Typically labeled 2HD - which means two-

sided, high density.• This disk can store 1.44 megabytes of data

– equivalent of 400 typewritten pages.

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Floppy Disks

• Has thin exterior jacket made of hard plastic to protect the flexible disk inside.

• Has a shutter that slides open to expose the disk surface.

• Read-write head from the disk drive moves across the exposed disk to store and retrieve data.

• When the notch is open, data cannot be stored on the disk.

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Floppy Disks• Tomorrow’s standard floppy disks – floppy-disk

cartridges• These are 3 ½ inch disks that are thicker and

require special disk drives.• The three best known floppy-disk cartridges are:• Zip Disks

– Produced by Iomega.– Have a 100 MB or 250 MB capacity (over 170 times as

much as today’s standard floppy).– Zip drives are standard on many of today’s more powerful

system units.– Disadvantage - Cannot read and store data on 1.44 MB

standard disk.

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Floppy Disks• SuperDisks

– Produced by Imation.– Have a 120 MB capacity.– Advantage - Can read and store data on 1.44 MB standard

disk.

• HiFD Disks– From Sony Corporation.– Have a 200 MB capacity (greater than SuperDisk).– Advantage – Can read and store data on 1.44 MB standard

disk.

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Hard Disks

• A hard disk is another type of permanent storage.

• Hard disks use thick, ridged metallic platters as their storage media.

• They are able to store and retrieve information much faster than floppy disks.

• They have a greater storage capacity than floppy disks.

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Hard Disks

• Hard Disk Crash– The read-write head of a hard disk drive rides on a

cushion of air about 0.000001 inches thick.– The cushion of air is so thin that certain

circumstances make the disk vulnerable to data loss.

– Smoke particles, fingerprints, dust, or human hair can come between the read-write head and the magnetic disk surface.

– This could cause some or all of the data on the disk to be destroyed and is referred to as a disk head crash.

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Hard Disks• Internal Hard Disk

– also known as a fixed disk– located inside the system unit and cannot be

removed– has one or more metallic platters sealed inside a

container called the disk drive– contains the motor for rotating the disks, access

arms, and read-write heads for every platter– typical hard drive is composed of four 3-½ inch

metallic platters– Advantages over floppy:

• capacity and speed• Can hold as much information as 56,000 standard floppy

disks

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Hard Disks

• Hard-Disk Cartridge – easy to remove as a cassette from a videocassette

recorder.– used primarily to complement an internal hard disk– particularly useful to protect or secure sensitive

information– provide a computer with an unlimited amount of

permanent storage.– typical capacity is 2 gigabyte per cartridge.

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Hard Disks• Hard-Disk Pack

– composed of several platters aligned one above the other

– pack can be removed from the computer– has access arms with two read-write heads, to

read the surface above one, and one below– used to store a massive amount of information– used by banks and credit card companies to

record financial information– provide a computer with an unlimited amount of

permanent storage.

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Computer Access Time– It is the time between the computer’s request for

data from secondary storage and the completion of the data transfer.

– The time factor between the computer’s request for data from secondary storage and the completion of the data transfer.

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Hard Disk Performance• There are three ways to improve the performance

of hard disks:• Disk Caching

– Disk caching improves performance by anticipating data needs.

– It requires a combination of hardware and software.– Frequently used data is read from the hard disk into cache

memory during idle processing.– Data is then accessed directly from cache memory to RAM

memory when needed.– The transfer rate from cache memory is faster than from the

hard disk.– System performance can increase as much as 30 percent

using disk caching.

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Hard Disk Performance• RAIDs (Redundant Arrays of Inexpensive

Disks)– RAIDs are inexpensive hard-disk drives grouped

together using networks and special software.– They improve hard disk performance by expanding

external disk storage.– The grouped disks are treated as a single large-

capacity hard disk.– RAIDs can outperform single disks of comparable

capacities.

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Hard Disk Performance• File Compression

– File compression can increase storage capacity by reducing the amount of space required to store data and programs.

– File compression can be used with hard or floppy disks.– It helps to speed the transmission of files from one computer

to another.– It is the common file transfer activity over the Internet.– File compression replaces repeated bit patterns with a token

symbol to reduce space.– Files can be shrunk to a quarter of original size using file

compression.– Files can be decompressed back to original file with

decompression software.

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• Permanent storage media that use laser technology to store data

• The laser is used to alter the surface of a plastic or metallic disk to represent binary code.

• Flat areas (lands) and bumpy areas (pits) on the disk surface represent the 0s and 1s.

• The disk is then read by a laser that projects a tiny beam of light on these areas.

Optical Disks

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• Optical disks can be 3½, 4¾, 5¼, 8, 12 and 14 inches.

• Most common size of optical disk is 4¾ inch.• Optical disks can typically hold over 17

gigabytes of data (several million typewritten pages).

• There are two common formats of optical disks:– CD (Compact Disc)– DVD (Digital Versatile Disc or Digital Video Disc)

Optical Disks

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Compact Disc Features

• CDs are the most widely used optical disk format.

• This format can store 650 megabytes of data on one side of the disk.

• Its rotation speed determines how fast data can be transferred from the disk.

• Examples: • 24X = 3.6 MB per second• 32X = 4.8 MB per second

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CD-ROM• The three basic types of CDs are:• CD-ROM (Compact Disc-Read Only Memory)

– Similar to a commercial music CD.– Cannot be written on or erased by user.– Used to distribute large databases and references.

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CD-R & CD-RW

• CD-R (Compact Disc-Recordable)– Can be written to once but read many times.– Also known as WORM (Write Once, Read Many times).– Used to archive or permanently store large amounts of

information.– Used to create custom music CDs (see Making IT Work

for You: CD-R Drives and Music from the Internet) and to archive data.

• CD-RW (Compact Disc-Rewriteable)– Also known as erasable optical disk.– Disk surface is not permanently altered when data is

recorded.– Can be written on, erased, and then written on again.– Used to create and edit multimedia presentations.

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DVD• DVDs are also known as Digital Video

Disc.

• They can store 17 gigabytes on one side of the disk (more than 30x CD disk).

• Many DVD discs can store data on both sides of the disk, doubling the capacity.

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DVD• DVD-ROM (Digital Versatile Disc-Read Only

Memory)– Cannot be written on or erased by user.– Can provide over two hours of very high quality video and

sound.• DVD-R (Digital Versatile Disc-Recordable)

– Can be written to once but read many times.– Used to create permanent archives for large amounts of

data.– Not as widely used as CD-R discs because of their higher

costs.• DVD-RAM (Digital Versatile Disc-Random Access

Memory) and DVD-RW (Digital Versatile Disc-Rewriteable)

– Two types of reusable DVD disks.– They can be used over and over again on a variety of

applications.

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DVD

• DataPlay– This is a new optical disk the size of a quarter.– It has a capacity of 500 MB.– This disk is capable of holding five hours of CD quality

sound.– It will become widely used for specialized applications

such as storing digital photographs and music for portable players.

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Magnetic Tape• Form of permanent storage media• Stores data in sequential access only, that

is, one after another• Once data is stored on tape, access to the

data is always sequential, starting at the beginning of the tape and working through until the data is found.

• Sequential access takes more time to access specific information.

• Magnetic tape is almost exclusively used for backup purposes today.

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Magnetic Tape• There are two forms of magnetic

tape storage:

• Magnetic Tape Streamers – used with microcomputers.

• Magnetic Tape Reels – used with minicomputers and mainframes.

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Magnetic Tape• Internet Hard Drives• These are also known as idrive or online

storage.• They provide users with free or low-cost

storage.• A user can access stored information from

any computer connected to the Internet• They are typically used as a specialized

secondary storage device.• Not for storing highly personalized or

sensitive information.

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Magnetic Tape• Solid-State Storage• Solid –state has no moving parts.• Information is stored and retrieved

electronically.• This storage is more expensive than other

storage but is also more reliable and requires less power.

• Flash memory cards are solid-state storage devices used in notebook computers.

– Flash memory is used in specialized input devices to capture and transfer data to desktop computers. Examples of uses are storage and transfer of digital camera images and recording and transfer of MP3 music files.