Lecture 11

RISC/CISC

Two types of CPU are currently popular. At the moment RISC CPUs are faster and cheaper to make than CISC CPUs. CISCs are currently not far behind in performance and are more popular because of compatability with previous CPUs.

Making the CPU faster.

How to measure the speed of a computer?
  1. Clock Rate
  2. Million Instructions Per Second (MIPS)
  3. Benchmarks
    1. Synthetic - test programs
    2. Real - real applications
At present, improvements in technology make the clock rates about twice as fast every two years. This is mainly due to increased miniturisation - Clock 10,20,40,80,160,320 MHz.

If fact CPUs are getting twice as fast every 1.5 years. The reason for this, is improvements in Computer Architecture.

These techniques allow the CPU to perform operations in parallel - parallel processing or parallelism.

When parallelism is applied at the level of the workings of the CPU it is called fine grained parallelism.

Multiprocessing.

There is a limit to how fast a computer can be made by increased miniturisation and fine grained parallelism. We have not yet reached that point but many people think we soon will. In order to make machines faster still coarse grained parallelism is necessary. This type of parallel processing involves using multiple CPUs in one computer.

Summary of topics covered so far