2.15 Module 16: advanced architectures  (Page 23/2)

1. introduction

In the previous sections of this course. we have concentrated on singleprocessor architectures and techniques to improve upon their performance, such as:

– Efficient algebraic hardware implementations

– Enhanced processor operation through pipelined instruction execution and multiplicity of functional units

– Memory hierarchy

– Control unit design

– I/O operations

Through these techniques and implementation improvements, the processing power of a computer system has increased by an order of magnitude every 5 years. We are (still) approaching performance bounds due to physical limitations of the hardware.

• Several approaches of parallel computer are possible

– Improve the basic performance of a single processor machine

Architecture / organization improvements

Implementation improvements

SSI -->VLSI -->ULSI

Clock speed

Packaging

– Multiple processor system architectures

Tightly coupled system

Loosely coupled system

Distributed computing system

- Parallel computer: SIMD computer, MIMD computer

2. multiple processor systems

System with multiprocessor CPUs can be divided into multiprocessor and multicomputers. In this section we will first study multiprocessors and then multicomputers

Shared-memory multiprocessor

A parallel computer in which all the CPUs share a common memory is called a tightly coupled systems

Figure 16.1. Tightly coupled systems, Shased-memory multiprocessor

• The features of the system are as follow.

– Multiple processors

– Shared, common memory system

– Processors under the integrated control of a common operating system

– Data is exchanged between processors by accessing common shared variable locations in memory

– Common shared memory ultimates presents an overall system bottleneck that effectively limits the sizes of these systems to a fairly small number of processors (dozens)

Message-passing multiprocessor

A parallel computer in which all the CPUs has a local independent memory is called a loosely coupled systems

Figure 16.2. Loosely coupled systems, Message-passing multiprocessor

• The features of the system are as follow.

– Multiple processors

– Each processor has its own independent memory system

– Processors under the integrated control of a common operating system

– Data exchanged between processors via interprocessor messages

– This definition does not agree with the one given in the text

Distributed computing systems

Now we can see the message-passing computer that multicomputer are held togerther by network.

– Collections of relatively autonomous computers, each capable of independent operation

– Example systems are local area networks of computer workstations

+ Each machine is running its own “copy” of the operating system

+ Some tasks are done on different machines (e.g., mail handler is on one machine)

+ Supports multiple independent users

+ Load balancing between machines can cause a user’s job on one machine to be shifted to another

Performance bounds of multiple processor systems

• For a system with n processors, we would like a net processing speedup (meaning lower overall execution time) of nearly n times when compared to the performance of a similar uniprocessor system
• A number of poor performance “upper bounds” have been proposed over the years