Information Technology Reference
In-Depth Information
in the 1960s, I was expected to end each program with a particular
program instruction that invoked the right transition code. With
this instruction, the next program could be read easily. But if I omit
ted this instruction, the next user had to restart the computer before
his or her program could be read.
The pooling of instructions for common tasks and transitions
gave rise to the first operating systems. Over time, this collection of
common activities has expanded considerably, but the perspective
remains the same. An
operating system
is a program, or collection
of programs, containing instructions for coordinating computer us
age among users and for handling common tasks. Although details
vary from system to system, today's operating systems normally fa
cilitate the following general tasks:
Details of input and output
Administration of a system to allow multiple users to work
concurrently
Allocation (and deallocation) of main memory for different
users
Sharing of resources (e.g., files, printers) among several users
or machines
Communication among users and among machines
Mechanisms for protection and security of programs and
information
To clarify this list somewhat, consider a typical initial interac
tion we might have with a computer. After turning on the machine,
a window appears on many computers asking us to log on with our
username and password. Assuming we provide correct information,
we then see a display of various directories, files, or applications. If
our computer does not require us to log in, we might see this display
immediately. Up until this point, all of our interaction has been with
the operating system. One of the first goals of an operating system,
therefore, is to keep track of authorized users. Thus, it is responsi
ble for providing places to type name and password information,
for checking the correctness of this material, and for displaying our
working environment.
When we view the collection of directories and materials that
appears on our screen, many computers allow us to use the mouse
