Even before the first computer was conceptualized, data had already been
stored on hard copy medium and used with a machine. As early as 1801, the
punched card was used as a control device for mechanical looms. One and
one-half centuries later, IBM joined punched cards to computers, encoding
binary information as patterns of small rectangular holes. Today, punch
cards are rarely used with computers. Instead, they are used for a handful
of train tickets and election ballots. Although some may find it
surprising, a computer printout is another type of hard copy medium.
Pictures, barcodes, and term papers are modern examples of data storage
that can later be retrieved using optical technology. Although it
consumes physical space and requires proper care, non-acidic paper
printouts can hold information for centuries. If long-term storage is not
of prime concern, magnetic medium can retain tremendous amounts of data
and consume less space than a single piece of paper.
The magnetic technology used for computer data storage is the same
technology used in the various forms of magnetic tape from audiocassette
to videocassette recorders. One of the first computer storage devices was
the magnetic tape drive. Magnetic tape is a sequential data storage
medium. To read data, a tape drive must wind through the spool of tape to
the exact location of the desired information. To write, the tape drive
encodes data sequentially on the tape. Because tape drives cannot randomly
access or write data like disk drives, and are thus much slower, they have
been replaced as the primary storage device with the hard drive. The hard
drive is composed of thin layers of rigid magnetic platters stacked on top
of one another like records in a jukebox, and the heads that read and
write data to the spinning platters resemble the arm of a record player.
Floppy disks are another common magnetic storage medium. They offer
relatively small storage capacity when compared to hard drives, but unlike
hard drives, are portable. Floppy disks are constructed of a flexible
disk covered by a thin layer of iron oxide that stores data in the form of
magnetic dots. A plastic casing protects the disk: soft for the 51/4-inch
disk, and hard for the 31/2-inch disk. Magnetic storage medium, for all
its advantages, only has a life expectancy of twenty years.
Data can be stored on electronic medium, such as memory chips. Every
modern personal computer...