Information Technology Reference
In-Depth Information
Memory Management
The OS also controls how memory is accessed and maximizes available memory and storage.
Newer OSs typically manage memory better than older OSs. The memory-management
feature of many OSs allows the computer to execute program instructions effectively and to
speed processing. One way to increase the performance of an old computer is to upgrade to
a newer OS and increase the amount of memory.
Most OSs support virtual memory, which allocates space on the hard disk to supplement
the immediate, functional memory capacity of RAM. Virtual memory works by swapping
programs or parts of programs between memory and one or more disk devices—a concept
called paging. This reduces CPU idle time and increases the number of jobs that can run in
a given time span.
Processing Tasks
The task-management features of today's OSs manage all processing activities. Task man-
agement allocates computer resources to make the best use of each system's assets. Task-
management software can permit one user to run several programs or tasks at the same time
(multitasking) and allow several users to use the same computer at the same time (time-
sharing).
An OS with multitasking capabilities allows a user to run more than one application at
the same time. Without having to exit a program, you can work in one application, easily
pop into another, and then jump back to the first program, picking up where you left off.
Better still, while you're working in the foreground in one program, one or more other ap-
plications can be churning away, unseen, in the background , sorting a database, printing a
document, or performing other lengthy operations that otherwise would monopolize your
computer and leave you staring at the screen unable to perform other work. Multitasking
can save users a considerable amount of time and effort.
Time-sharing allows more than one person to use a computer system at the same time.
For example, 15 customer service representatives might be entering sales data into a computer
system for a mail-order company at the same time. In another case, thousands of people
might be simultaneously using an online computer service to get stock quotes and valuable
business news.
The ability of the computer to handle an increasing number of concurrent users smoothly
is called scalability . This feature is critical for systems expected to handle a large number of
users, such as a mainframe computer or a Web server. Because personal computer OSs usually
are oriented toward single users, they do not need to manage multiple-user tasks often.
Networking Capability
Most operating systems include networking capabilities so that computers can join together
in a network to send and receive data and share computing resources. PCs running Mac,
Windows, or Linux operating systems allow users to easily set up home or business networks
for sharing Internet connections, printers, storage, and data. Operating systems for larger
server computers are designed specifically for computer networking environments.
Access to System Resources and Security
Because computers often handle sensitive data that can be accessed over networks, the OS
needs to provide a high level of security against unauthorized access to the users' data and
programs. Typically, the OS establishes a logon procedure that requires users to enter an
identification code, such as a user name, and a matching password. If the identification code
is invalid or if the password does not match the identification code, the user cannot gain
access to the computer. Some OSs require that user passwords change frequently—such as
every 20 to 40 days. If the user successfully logs on to the system, the OS restricts access to
only portions of the system for which the user has been cleared. The OS records who is using
the system and for how long, and reports any attempted breaches of security.
 
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