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Prepared by
Md. Amirul Islam
Lecturer
Department of Applied Physics & Electronics
Bangabandhu Sheikh Mujibur Rahman Science &
Technology University, Gopalganj – 8100
A computer system consists of software (programs) and
hardware (the physical machine and its electronic components).
The operating system software is the chief piece of software, the
portion of the computing system that manages all of the
hardware and all of the other software. To be specific, it controls
every file, every device, every section of main memory, and
every nanosecond of processing time. It controls who can use the
system and how. In short, it’s the boss.
Each time the user sends a command, the operating system
must make sure that the command is executed; or, if it’s not
executed, it must arrange for the user to get a message
explaining the error. This doesn’t necessarily mean that the
operating system executes the command or sends the error
message—but it does control the parts of the system that do.
An operating system is similar to a government. Like a
government, it performs no useful function by itself. It
simply provides an environment within which other
programs can do useful work.
Fig – 1: Model of a non-networked operating
system shows four subsystem managers
supporting the User Interface.
Fig – 2: Networked systems have a Network Manager
that assumes responsibility for networking tasks while
working harmoniously with every other manager.
The pyramid shown in Figure-1 is an abstract representation of an
operating system and demonstrates how its major components work
together. At the base of the pyramid are the four essential managers
of every operating system. these managers are the basis of all
operating systems.
Each of the subsystem managers, shown in Figure – 1 or
Figure – 2, must perform the following tasks:
• Monitor its resources continuously
• Enforce the policies that determine who gets what, when,
and how much
• Allocate the resource when appropriate
• De-allocate the resource when appropriate
Xerox 8010 Star (released in 1981):
It was known as “The Xerox Star”, later renamed “ViewPoint”
and later again renamed to “GlobalView”.
OS/2 1.x (released in 1988): OS/2 was originally co-developed by
IBM and Microsoft, but in 1991 the two companies split up, with
Microsoft incorporating the technology in its own Windows GUI
and IBM developing OS/2 further.
KDE 1.0 (released in 1998):
This is how the KDE team described the project upon releasing
version 1.0: “KDE is a network transparent, contemporary
desktop environment for UNIX workstations.
GNOME 1.0 (released in 1999):
GNOME desktop was mainly developed for Red Hat Linux,
later it was developed for other Linux distributors as well.