V22.0436 - Prof. Grishman

Lecture 20: CPU Performance, cont'd; Memory Technology

Pipelining, cont'd

Pipelining is more complex for CISC machines, because the instructions may take different lengths of time to execute. However, RISC-style pipelining is now incorporated into high-performance CISC processors (such as the Pentium) by treating the simple CISC instructions like RISC operations, and breaking the more complex CISC instructions into a sequence of RISC-like operations.

Taking advantage of technology improvements

How has the steady progress in integrated circuit technology been translated into improvements in processor performance?

The technology improvements lead to faster transistors and smaller transistors. Faster transistors mean faster clock times. Smaller transistors mean that we can put more transistors on a chip. What can we do with the increasing number of transistors to improve performance?

All of these techniques can be observed in the progress of x86 implementations:

At some point most of these methods have diminishing returns. Then need to consider use of multiprocessors to improve performance, even though this adds to software complexity. Many systems now use large collections of workstations as the most effective approach for high-performance computing.

Memory Technology

Early technologies: delay line; magnetic core (dominant mid-50's to mid-70's)

Primary technology today: transistor RAM

static RAM:

dynamic RAM:

For some applications, memory does not have to change --- use ROM (read-only memory).

Static and dynamic RAM are both volatile: data disappears when power is lost. For some applications, data must be preserved, so a special (slow) non-volatile RAM is used.