Information Technology Reference
In-Depth Information
simple, effective, and efficient processing on many types of comput
ers. In this environment, researchers needed to be able to share in
formation and combine various programs into larger tasks. In
achieving this work environment (or virtual machine), Unix empha
sized terse, powerful commands based on textual input. In contrast,
the first versions of the Macintosh operating system emphasized a
graphicsbased virtual machine, containing pictures of files and pro
grams. Rather than typing text to combine commands on a single
line, Macintosh users took advantage of a mouse to issue simple
commands to start various applications.
With different design objectives, operating systems developed in
different directions, with different strengths and capabilities. Even
with their different initial perspectives, however, the operating sys
tems have not stayed static. Rather, each operating system has
evolved in remarkable ways, and capabilities from one system have
been adapted for another. For example, as computer users grew to
appreciate the graphical interfaces on the Macintosh and other sys
tems, both Microsoft and Unix found ways to incorporate those
features into their own products. Today, operating systems may
have some common capabilities, but behind the scenes they achieve
those features differently.
Altogether, the varying needs and priorities of users have
prompted multiple approaches for handling common computing
tasks, and these perspectives have led to different operating systems.
Most computers have only one CPU, so they can do only one
thing at a time. Historically, a computer would first work on one
task until it was done before moving on to another task. As an ex
ample in a reasonably modern context, if you were editing a docu
ment using a word processor, then no other work could be done on
your computer at the same time. When you wanted to print the doc
ument, then printing was the only task allowed. This meant that
you could not continue to work on the document while you were
printing it. When the CPU was devoted to printing, it could not also
handle other processing requests. Such an environment is said to
support single tasking, and this approach was widespread in early
computers.
