1. Introduction

1. Introduction
	Chapter 7. Parallel Machines

Introduction
Definition:
Parallel machines are computers that can execute more than one program instruction at the same time.
Types of parallel hardware:
- SISD Single Instruction Single Data (mainframes)
- SIMD Single Instruction Multiple Data (array processors)
- MISD Multiple Instruction Single Data (none)
- MIMD Multiple Instruction Multiple Data (transputers)
MIMD: It is the most used parallel system.
Figure 7.1. MIMD
Tightly Coupled Systems
CPUs share the same memory.
- High bandwidth.
- Close integration.
- Used in main stream market (Intel, Sparcs, Power PC, etc).
Bus systems:
Figure 7.2. Bus System
The CPUs are connected to the shared memory through a bus.
Advantages:
- Most used configuration (off the shelf chips).
- Low cost.
- Simpler software design.
- Unified main memory.
Disadvantages:
- Number of CPUs is limited by bus bandwidth.
- Requires an expensive bus (wide and fast) for great numbers of CPUs.
- Cache coherence problems.