Page 27 - DCAP403_Operating System

Operating System

Notes Figure 2.3: Multiprogramming

Program 1 Program 2

Idle Idle Idle Idle
P1 P1 P1 P2 P2 P2

(a) Sequential Execution

Program 1
P1 P1 P1

Program 2

(b) Execution in Multiprogramming Environment
When that program needs to wait for some 110 operation, it switches over to program 3 and so
on. If there is no other new program left in the main memory, the CPU will pass its control back
to the previous programs.

Multiprogramming has traditionally been employed to increase the resources utilisation of a
computer system and to support multiple simultaneously interactive users (terminals).

Multiprocessing System

A multiprocessing system is a computer hardware configuration that includes more than one

independent processing unit. The term multiprocessing is generally used to refer to large

computer hardware complexes found in major scientific or commercial applications.
A multiprocessor system is simply a computer that has >1 & not <=1 CPU on its motherboard. If
the operating system is built to take advantage of this, it can run different processes (or different
threads belonging to the same process) on different CPUs.
Today’s operating systems strive to make the most efficient use of a computer’s resources.

Most of this efficiency is gained by sharing the machine’s resources among several tasks
(multi-processing). Such “large-grain” resource sharing is enabled by operating systems without
any additional information from the applications or processes. All these processes can potentially
execute concurrently, with the CPU (or CPUs) multiplexed among them. Newer operating
systems provide mechanisms that enable applications to control and share machine resources at
a finer grain-, that is, at the threads level. Just as multiprocessing operating systems can perform

more than one task concurrently by running more than a single process, a process can perform
more than one task by running more than a single thread.

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