Floppy Disks
and Hard Disks
The data and information used in a computer needs
to be stored for future use. The memory of a computer only holds items
temporarily while they are being processed. When not being processed, these
items must be stored in auxiliary storage devices. These devices include floppy
disks, hard disks, CD-ROM, and DVD-ROM. When selecting a storage device it is
important to know that each device holds different amounts of information.
Although floppy disks once were available in two
sizes, the 5.25-inch floppy disk rarely is used today, and some believe it is
destined for the same fate as the eight-track tape. Because of its rigid
plastic shell, it may be difficult to see the 3.5-inch disk as
"floppy." The name is justified, however, not only by the disk's
ancestry but also by the flexible character of the disk itself. When a floppy
disk drive is reading from or writing to a floppy disk, a light turns on next
to the drive. Floppy disks never should be inserted into or removed from the
drive when this light is on. Most magnetic disks are read/write storage media.
Some optical discs, such as CD-ROMs, usually can be read from but not written
to. Each track on a formatted floppy disk is very narrow. To see how narrow,
try to draw 80 lines in a 11/4-inch space (the approximate radius of the floppy
disk surface). Floppy disks are soft-sectored, meaning that the number of
sectors is not predetermined. Floppy disk access time depends on the time
needed to locate the correct track, the time required to rotate the disk to the
proper sector, and the time necessary to transfer the data into main memory.
Although personal computer hard disks usually are
fixed (i.e., not removable), some portable computers have removable hard disk
drives. Unlike floppy disks, hard disks constantly are spinning, at a rate 10
to 20 times faster than floppy disks. Therefore, access time for hard disks is
significantly less than access time for floppy disks. While a floppy disk
read/write head rests on the disk, the read/write head for a hard disk hovers
about 10 millionths of an inch above the disk surface. Contamination on the
disk - a speck of dust (about 1550 millionths of an inch), a fingerprint (about
600 millionths of an inch), or a particle of smoke (about 250 millionths of an
inch) - can cause a "head crash," destroying data and rendering the
disk drive unusable. For this reason, hard disk drives are sealed and
manufactured in an environment that typically is cleaner than a hospital
operating room. Storage capacity can be increased on both hard disks and floppy
disks with compression programs such as Stacker, WinZip, or PKZIP.
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