Information Technology Reference
In-Depth Information
Although single tasking is conceptually simple, in practice it
leaves the CPU idle at times. For example, printing requires paper
to move through a printer, and the singletasking CPU has to wait
for the paper movement. Similarly, the CPU can execute program
instructions much faster than a typist can type, so the CPU that uti
lizes single tasking is idle if it has to wait for information from a
typist. In general, I/O devices usually involve some mechanical ac
tivity and thus work much more slowly than an electricitybased
CPU. In singletasking computers, therefore, the CPU generally has
to wait for information from I/O devices.
Rather than waste CPU capabilities,
multitasking
allows a com
puter to coordinate the processing of several tasks at once. For ex
ample, while the CPU waits for I/O for one task, it might make
progress on the work for another task. Similarly, if several user tasks
require computational work, the CPU may take turns. It makes some
progress on a first task, then on a second, then on a third, and so on,
until each desired task has had some attention. This may finish some
work, but additional work may remain. So, in a second round, the
CPU may go back to the first task for some additional work, and
then continue processing on the second and later tasks. In a third
round, again the CPU gives each task additional attention.
Overall, with the CPU's activity split among several projects, the
progress on any one project may be slower than if that task received
exclusive CPU attention. However, because a CPU works quickly, a
user may not notice any slowdown for relatively simple tasks. For
example, because interactions with a printer and editing a document
are each relatively straightforward, a multitasking environment
would allow each to take place at the same time. (In both cases, the
limiting factors are likely to be the movement of paper through the
printer and the speed at which a typist can enter data, and the CPU
is likely to be able to do all required processing for either of these
tasks while it is waiting for action from the other.)
On the other hand, even a multitasking environment can proceed
only as fast as its CPU allows. Thus, if a user is doing an extensive
computation in a spreadsheet and also editing a large document (that
requires extensive virtual memory), then the user may notice a signif
icant deterioration in speed from the norm in both applications.
For the most part, we can appreciate multitasking, because it al
lows us to shift our attention from one task to another or from one
window to another. However, because all of our work competes for
