Computer Studies Today Chapter 18

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» Two main types of secondary storage devices:

– Magnetic storage devices

– Optical storage devices

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Floppy Disks

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» Data are organised on a floppy disk in rings called tracks.

» Each track is divided into sectors.

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» A floppy disk drive allows data to be read from or written to a floppy disk.

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Hard Disks

A hard disk and a hard-disk drive

A disk pack

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» The mechanism for reading or writing data on a hard disk is similar to that of a floppy disk.

» The hard disk consists of several metallic platters and the drive has several access arms.

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» The access arms move several read-write heads in and out between the hard disks.

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» A way to organise data on a disk pack is the cylinder method.

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» Materials that can cause a head crash.

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» Hard disks have TWO advantages over floppy disks:

– Hard disks provide larger capacities than floppy disks.

– The access time for a hard disk is shorter.

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» The access mode of magnetic disks (floppy disks and hard disks) is direct access.

» Data are recorded on or retrieved from the disks randomly.

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Magnetic Tape

A cartridge tape and a cartridge tape unit

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» Magnetic tape is the cheapest secondary storage medium and is suitable for storing a large amount of data.

» Data are recorded on or retrieved from the tapes sequentially.

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Optical Disks

A CD-ROM driveOptical disks

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» The access mode of optical disks is direct access.

» The storage capacity of optical disks is enormous and much larger than that of floppy disks.

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» Comparisons between floppy disks, hard disks, magnetic tapes and optical disks: