Microsoft Office Tutorials and References
In Depth Information
COM 13
STORAGE DEVICES
platter, two surfaces are available for data. If the drive uses two platters, four sets of read/write
heads read and record data from the four surfaces. Storage capacities of internally mounted fixed
disks for personal computers range from 10 GB to more than 750 GB.
The system unit on most desktop and notebook computers contains at least one hard disk.
Although hard disks are available in removable cartridge form, most hard disks cannot be
removed from the computer.
F LOPPY D ISKS Another older form of magnetic storage is the floppy disk ,or diskette ,an
inexpensive portable storage medium (Figure 18a). The most widely used floppy disk is 3.5 inches
wide and typically can store up to 1.44 megabytes of data, or 1,474,560 characters. Although the
exterior of the 3.5-inch disk is not floppy, users still refer to them as floppy disks. Floppy disks are
not as widely used as they were 15 years ago because of their low storage capacity.
A floppy disk drive is a device that can read from and write on a floppy disk. Floppy disk
drives are either built into the system unit (Figure 18a) or are external to the system unit and
connected to the computer via a cable (Figure 18b).
Data stored on a floppy disk must be retrieved and placed into memory to be processed. The
time required to access and retrieve data is called the access time . The access time for floppy
disks varies from about 175 milliseconds to approximately 300 milliseconds (one millisecond
equals 1/1000 of a second). On average, data stored in a single sector on a floppy disk can be
retrieved in approximately 1/15 to 1/3 of a second.
On a personal computer, you insert and remove a floppy disk from a floppy disk drive.
FIGURE 18
(a) Floppy disk drive installed inside a
desktop computer
(b) External floppy disk
drive attached to computer
with a cable
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