Measuring
Performance
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Computer Performance
Measuring Computer Performance
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Clock Speed
MIPS
FLOPS
Benchmark Tests
Factors Affecting Computer Performance
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Processor Speed
Data Bus Width
Amount of Cache
Faster Interfaces
Amount of memory
3 Computer Performance
3.2 Measuring Performance
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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 Performance
3.2.1 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
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3 Computer Performance
3. 2 Measures of Processor Speed
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Clock Speed
– Generally the faster the clock speed the faster the processor
– 3.2 GHz is faster than 933 MHz
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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.
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Flops – Floating Point Operations per sec.
– Best measure as FP operations are the same in every
processor and provide best basis.
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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 Performance
3.3.1 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.
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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.
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Width of Address bus affects the amount of
memory which can be accessed.
3 Computer Performance
3.3.2 Peripherals & System Performance
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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 Performance
3.3 Memory & System Performance
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Speed of access & Word size
– 15-120 nanosecond but memory speed and word
size dictated by motherboard and processor
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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.