Multiprocessors

Characteristics of multiprocessors

A multiprocessor system is an interconnection of two or more CPUs with memory
and input-output equipment. The term “processor” in multiprocessor can mean either a central processing unit (CPU) or an input-output processor (IOP).

Multiprocessors are classified as multiple instruction streams, multiple data stream
(MIMD) systems

The similarities and distinctions between multiprocessors and multicomputers are
Similarity

• Both support concurrent operations

Distinction

• The network consists of several autonomous computers that may or may not communicate with each other.
• A multiprocessor system is controlled by one operating system that provides interaction between processors and all the components of the system cooperate in the solution of a problem.

 Multiprocessing improves the reliability of the system.
 The benefit derived from a multiprocessor organization is an improved system
performance.
o Multiple independent jobs can be made to operate in parallel.
o A single job can be partitioned into multiple parallel tasks.
 Multiprocessing can improve performance by decomposing a program into
parallel executable tasks.
o The user can explicitly declare that certain tasks of the program be
executed in parallel.
 This must be done prior to loading the program by specifying the
parallel executable segments.
o The other is to provide a compiler with multiprocessor software that can
automatically detect parallelism in a user’s program.
 Multiprocessor are classified by the way their memory is organized.
o A multiprocessor system with common shared memory is classified as a
shared-memory or tightly coupled multiprocessor.
 Tolerate a higher degree of interaction between tasks.
o Each processor element with its own private local memory is classified as
a distributed-memory or loosely coupled system.
 Are most efficient when the interaction between tasks is minimal