Storage Devices

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Contents

• Storage

• Primary

• Secondary

• Access Method

• Floppy disk

• Hard disk

• Optical disks

• Magnetic media

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Overview

Information storage For future To share To modify

Permanent Storage secondary

storage, nonvolatile

Temporary storage RAM volatile

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Secondary Storage

1. Secondary storage provides permanent or non-volatile storage:

2. This is accomplished by writing files to and reading from the secondary storage device.

• Writing- Is the process of serving information to the secondary storage device.

• Reading- Is the process of accessing information from secondary storage.

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Characteristics of Secondary Storage devices

• Media or medium which is the actual physical material that holds the data and programs

• Capacity measures how much a particular storage medium can hold

• Storage device are hardware that reads data and programs from storage media. Most also write to storage medium

• Access speed or access time measures the amount of time required by the storage devices to retrieve data and program.

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Storage devices can be categorized as magnetic or optical

Magnetic storage are such as diskettes, hard disk, high capacity floppy disks, and magnetic tapes

Optical storage are compact disks CD-ROM, DVD-ROM, CD-R, CD-RW etc

Categories of Storage Devices

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Floppy Disks

• Floppy disks are often called diskettes or simply disks.

• They are portable and removable storage media

• They use flat circular pieces of Mylar plastic that have been coated with magnetic material.

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Traditional Floppy Disk

Traditional floppy disks:

1.44MB

3.5 inch

2HD-two side high density

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How a Disk Drive Works

Metal shutter

Hard plastic jacket

Label

Write protection notch in the open position

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Hard Disks

Metallic disks Composed of metallic rather than plastic disks Fast information storage and retrieval (write and

read) Read-write heads

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Materials that can cause a Materials that can cause a head crashhead crash

Materials that can cause a Materials that can cause a head crashhead crash

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Internal Hard Disk Inside system unit for storing the

operating system, other programs and large data files.

Motor with access arm and read-write heads.

Many advantages over floppy disks. Capacity (up to thousands

times a single floppy) Speed (twenty times the

speed)

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Hard-Disk Packs

Removable, massive storage capacity

Common in mainframes Resembles stack of record albums

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Optical disks use laser technology. CD and DVD are optical disk formats.

Compact, high capacity form of permanent storage

Laser beam writes by creating a pattern of pits (holes) and lands (flat areas) to encode data bits

Laser beams reflect off the pits and lands to read the data

Optical Disks

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CD-ROM

Compact disc-read-only memory

Not written to

650 MB capacity

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CD-R & CD-RW

CD-Recordable or WORM

(write once, read many)

CD-RW or rewritable optical discs

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DVD

Digital Versatile Disk or Digital Video Disk

Up to 4.7 gigabytes a capacity, seven times CD DVD-ROM- provide high quality, movie length videos

DVD-R- consumer recordable version

DVD-RAM or DVD-RW- rewritable version of 2.6 to 5.2 GB storage capacity

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Magnetic Tape

Disks offer fast, direct access to data programs Tapes offer sequential access (fast forwarded or rewound)

Storage and backup Forms of tape storage are:

Magnetic tape streamers Magnetic tape reels

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Backup tape cartridge units used with

microcomputer systems

Capacities range from 120 MB to 5 GB

Magnetic Tape Streamers

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Magnetic Tape Reels

Used with minicomputer and mainframe

computers

Often 1/2 inch wide and 1/2 mile long

Stores 1600 to 6400 characters per inch

Tapes are run on magnetic tape drives or

magnetic tape units

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