computer studies today chapter 18 1 »two main types of secondary storage devices: –magnetic...
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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: