Measuring Performance

Computer Performance Measuring Computer Performance

– Clock Speed– MIPS– FLOPS– Benchmark Tests

Factors Affecting Computer Performance– Processor Speed– Data Bus Width– Amount of Cache– Faster Interfaces– Amount of memory

3 Computer Performance3.2 Measuring Performance

When we measure performance we usually mean how fast the computer carries out instructions. The measure we use is MIPS, millions of instructions per second.

MIPS affected by– The clock speed of the processor– The speed of the buses– The speed of memory access.

3 Computer Performance3.2.1 The Clock

Every processor has a clock which ticks continuously at a regular rate.

Synchronises all the components. Cycle time measured in GHz 200 MHz (megahertz) means the clock

ticks 200,000,000 times a second (Pentium1 -1995)

2.7 – 4+ GHz in 2010

3 Computer Performance3. 2 Measures of Processor Speed

Clock Speed– Generally the faster the clock speed the faster the processor

– 3.2 GHz is faster than 933 MHz Mips – Millions of Instructions per Second

– Better comparison but beware of false claims e.g. only using the simplest & fastest instructions and different processor families.

Flops – Floating Point Operations per sec.– Best measure as FP operations are the same in every

processor and provide best basis. Benchmark Tests

– Well defined standardised routines to test the performance of a computer.

• Dhrystone – tests string and frequently used functions• Whetstone – test using arithmetic functions

3 Computer Performance3.3.1 Data Bus Width A WORD is the number of bits a processor

can handle in one operation.– If word size and data bus same size then data

transfers carried out in single operation. Width of data bus defines how much data

can be carried in one fetch.– 32 bit data bus (word length) carries twice as

much data as a 16 bit bus and a 32 bit system should be faster.

– Most modern processors use 32 bit but some (AMD) 64 bit.

Width of Address bus affects the amount of memory which can be accessed.

3 Computer Performance3.3.2 Peripherals & System Performance

Peripherals work at much slower speeds than the CPU.– Buffers and spooling can help.– Sound cards can have their own

processor, RAM and ROM.– Video cards their own RAM (up to 1Gb)

3 Computer Performance3.3 Memory & System Performance

Speed of access & Word size– 15-120 nanosecond but memory speed and word size dictated

by motherboard and processor Amount of memory

– Adding memory (upgrade) usually improves system performance esp. graphics & multimedia.

– Usually 2 slots on motherboard so max memory is 2 x largest modules (currently 4Gb affordable).

Cache (pronounced cash) memory– Cache exists between memory and processor– Very fast memory speeding data transfer in shorter fetch cycle.– Currently 2Mb Cache common

Now Answer the following questions in your jotter …..

1. a) Explain what effect increasing the width of the address bus will have on system performance

b) Explain what effect increasing the width of the data bus will have on system performance

2. How many gigabytes of memory would a 40 bit address bus be able to address if the data bus length was :

a) 8 bits

b) 16 bits?

3. a) What is meant by the CLOCK Rate of a processor?

b) What unit is used to measure clock rate?

4. a) Give 2 reasons why adding more main memory can improve system performance

b) Give 2 reasons why adding more cache memory can improve system performance

5. Abdul has a 2.5GHz PowerPC and Sarah has a 2.7 GHz CompaqPC. Sarah says her computer is faster than Abdul’s because it has a higher clock rate.

a) Do you think this is true?

b) Describe a test that could be done to see if she is correct.