History

Von Neumann Machine

Utilises the stored program concept - First published in 1945 by John von Neumann
Completed in 1952, the IAS computer is the prototype for all subsequent general-purpose computers

Structure

• Main memory - for storing programs alongside data
• An Arithmetic and Logic Unit (ALU) - capable of operating on binary data
• A Control Unit - interprets instruction in memory and executes them
• Input and Output - operated by the control unit

Design

The Bus

DEC PDP-8

1964
The DEC PDP-8 was the first minicomputer

• Didn't require an air-conditioned room
• Could sit on a lab bench / desk
• Cost only ~$16,000
  The DEC was the first commercial device to use a bus structure instead of switches

The Structure

Gordon Moore's Law

1965: Every year the number of transistors on a chip would double every year
1975: Every other year the number of...

In reality, it has been every 18 months

• The cost of a chip has remained relatively stable throughout the years
• Higher packing density means shorter electrical paths, giving higher performance
• Smaller size gives increased flexibility
• Power and cooling requirements are reduced
• Fewer interconnections reduces points of failure - improving reliability

Performance

• Processor speed is increasing
• Memory Capacity is increasing
• Memory speed lags behind processor speed

Performance Measures

• Various measures are used to assess performance - e.g. memory bandwidth, MIPS. MFLOPS
• The maximum possible will be the value advertised
• Speed often competes with size (or memory) and both must be balanced against cost
• Software availability, ease of maintenance, etc. are also important