Module I Overview of Computer Architecture and Organization

Module I Overview of Computer Architecture and Organization

Performance Measure of Processor

Clock Speed • Speed of the processor is dictated by pulse frequency of clock • Clock signals are generated by a quartz crystal which generates a constant signal wave when power is applied. This wave is converted to digital voltage and is given to processor • Rate of pulses is clock rate or clock speed

Clock Speed • One increment of clock is clock cycle • Time between pulses is cycle time • Multiple instructions may get executed simultaneously, hence clock speed alone cannot define performance

Instruction Execution Rate • It is also called Average Cycles per Instruction(CPI) • Let CPIi be the no. of cycles required for instruction type i and Ii be the number of instructions executed of type i. • The average CPI is given as

Average Cycles per Instruction(CPI) • The processing time needed to execute a program can be expressed as • Processing time is influenced by 4 attributes – Design of instruction set – Compiler Technology – Processor Implementation – Cache and Memory hierarchies

Example

MIPS Rate • It is the rate at which instructions are executed. • It is Millions of Instruction Per Second • It is expressed as follows:

Problem 1 • Consider that the execution of a program results in the execution of 2 million instructions on a 400 MHz processor. The program consist of four major types of instruction. The instruction mix and the CPI of each type is given as follows:

Problem 1 Instruction Type CPI Instruction Mix Arithmetic and Logic 1 60% Load/Store (Cache hit) 2 18% Branch 4 12% Memory Reference(cache miss) 8 10%

Problem 2 • A benchmark program is run on a 40 MHz processor. The executed program consist of 100, 000 instruction executions, with the following instruction count and clock cycle count

Problem 2 Instruction Type Instruction Count CPI Arithmetic and Logic 45000 1 Data Transfer 32000 2 Floating Point 15000 2 Control Transfer 8000 2