Computer Organization and Architecture
Page 120
MULTIPROCESSORS: Characteristics of multiprocessors, interconnection structures, inter
processor arbitration, inter processor communication and synchronization, cache coherence,
shared memory multiprocessors.
Book: M. Moris Mano (2006), Computer System Architecture, 3rd edition, Pearson/PHI,
India: Unit-13 Pages: 489-514
Characteristics of Multiprocessors
A multiprocessor system is an interconnection of two or more CPU, with memory and
input-output equipment. As defined earlier, multiprocessors can be put under MIMD
category. The term multiprocessor is sometimes confused with the term multi computers.
Though both support concurrent operations, there is an important difference between a
system with multiple computers and a system with multiple processors.
In a multi computers system, there are multiple computers, with their own operating
systems, which communicate with each other, if needed, through communication links. A
multiprocessor system, on the other hand, is controlled by a single operating system, which
coordinate the activities of the various processors, either through shared memory or inter
processor messages.
The advantages of multiprocessor systems are:
· Increased reliability because of redundancy in processors
· Increased throughput because of execution of multiple jobs in parallel portions of the
same job in parallel
A single job can be divided into independent tasks, either manually by the programmer, or by
the compiler, which finds the portions of the program that are data independent, and can be
executed in parallel. The multiprocessors are further classified into two groups depending on
the way their memory is organized. The processors with shared memory are called tightly
coupled or shared memory processors.
The information in these processors is shared through the common memory. Each of
the processors can also have their local memory too. The other class of multiprocessors is
loosely coupled or distributed memory multi-processors. In this, each processor has their
own private memory, and they share information with each other through interconnection
switching scheme or message passing.