Microsoft Office Tutorials and References
In Depth Information
The other most common magnetic storage device is a hard disk drive , such as the one
shown in Figure 20. This drive contains several iron oxide-covered metal platters that are
usually sealed in a case inside the computer. Hard disk storage has two advantages over
floppy disk storage: speed and capacity.
Internal components of a hard disk drive
The speed of a disk drive is measured by its access time , the time required to read or
write one record of data. Access time is measured in milliseconds (ms), one-thousandths
of a second. The hard disk drive included in Figure 1, for instance, has 6 ms access time.
Its capacity is 80 GB. Although this seems like a very high number, a Windows-based
computer fully loaded with typical software can use up to 1 GB, and the addition of data
and multimedia files can add up quickly.
Another magnetic storage device is a tape drive , which provides inexpensive archival
storage for large quantities of data. Tape storage is much too slow to be used for day-to-day
computer tasks; therefore, tapes are used to make backup copies of data stored on hard
disks. If a hard disk fails, data from the backup tape can be reloaded on a new hard disk
with minimal interruption of operations. Large corporations use tape drives for backup, but
smaller companies and home computer systems rely on other storage methods.
Optical storage devices use laser technology to read and write data on silver platters. The
first standard optical storage device on personal computers was the CD-ROM drive, which
stands for Compact Disk Read Only Memory . One CD-ROM can store up to 700 MB,
equivalent to more than 450 floppy disks. Today’s personal computers are also equipped
with DVD , or Digital Video Disk , drives. DVDs, though the same size as CD-ROMs, can
store up to 4.7 GB of data, depending on whether data is stored on one or two sides of the
disk, and how many layers of data each side contains. This is a little less than seven times
the capacity of a CD. A DVD has more than enough storage capacity for an entire feature-
length film—up to 9 hours of video or 30 hours of CD-ROM-quality audio.
Optical storage technology records data as a trail of tiny pits in the disk surface. The data
that these pits represent can then be “read” with a beam of laser light. Figure 21 shows how
data is stored on optical media.