(2) Paper tape readers. With punched paper tape, data are again stored in
the form of the absence or presence of punched holes. These entries are permanent
and not reusable. Paper tape readers operate at approximately 100 characters per
second for mechanical readers and 1,000 per second for optical readers. Punched tape
can store small amounts of data in a more compact form than cards. It is relatively
inexpensive and the data can be seen (not so with magnetic tape, see next page).
Paper tape is most practical for use on small or time-shared terminals.
Figure 2-13. Reading head detects the presence or absence of a hole.
(3) Magnetic tape or magnetic disks. When magnetic media such as tape
or disks are used, data are entered in much the same way as with the keypunch. But it
is stored as magnetized spots on the surface of a tape or disk instead of punches on a
card. This is referred to as a key-to-tape system. The data can be stored indefinitely
because the spots retain their magnetism. Unlike punch cards, data can be replaced
with new data. Tape and disks can also store more data in a smaller space (6,250
characters per inch). Since data can be read into the CPU hundreds of times faster,
key-to-magnetic-tape-entry methods are more efficient than punch cards or paper and
are suitable for large volume, high-speed applications.
(a) Key-to-tape. Most key-to-magnetic tape systems are being
replaced by disks (hard disks) and diskettes (floppy disks) as a result of advancing
technology. Key-to-magnetic media represent an improvement over the slower punch
card and paper tape feeders. Speed has always been a concern because input (and
output) equipment has been a restraining factor on high speed computers since the
beginning. This is because data can be processed much more quickly than it can be
entered or written out.
(b) Key-to-disk systems. Atypical key-to-disk setup consists of several
keying devices, connected to a minicomputer. Data to be recorded onto magnetic disks
are usually first edited by a minicomputer. This editing is directed by the minicomputer's
stored-program instructions. The corrected data is then stored on the magnetic disk for
input to the computer.