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

LINUX Bash Shell

LINUX GUI Shell

MS DOS

UBUNTU

Windows7 (released 2009)

Mac OSX Mountain Lion

Xerox Alto, developed

in 1973.

Xerox 8010 Star (released in 1981):

It was known as “The Xerox Star”, later renamed “ViewPoint”

and later again renamed to “GlobalView”.

Apple Lisa Office System 1 (released in 1983)

VisiCorp Visi On

(released in 1984)

Mac OS System 1.0 (released in 1984)

Amiga Workbench 1.0

(released in 1985)

Windows 1.0x

(released in 1985)

GEM (released in 1985)

IRIX 3 (released in 1986, first release 1984)

GEOS (released in 1986)

Windows 2.0x (released in 1987)

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.

NeXTSTEP / OPENSTEP 1.0 (released in 1989)

OS/2 1.20 (released in 1989)

Windows 3.0 (released in 1990)

Windows 3.0 (released in 1990)

Amiga Workbench 2.04 (released in 1991)

Mac OS System 7 (released in 1991)

Windows 3.1 (released in 1992)

OS/2 2.0 (released in 1992)

OS/2 2.0 (released in 1992)

OS/2 2.0 (released in 1992) [2]

Windows 95 (released in 1995)

Windows 95 (released in 1995) [2]

OS/2 Warp 4 (released in 1996)

OS/2 Warp 4 (released in 1996)

Mac OS System 8 (released in 1997)

Windows 98 (released in 1998)

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.

Mac OS X (released in 2001)

Windows XP (released in 2001)

KDE 3 (released in 2002)

Windows Vista (released in 2007)

Mac OS X Leopard (released in 2007)

GNOME 2.24 (2008)

Windows7 (released 2009)

Mac OSX Mountain Lion (released 2012)

Windows 8 (released 2012)