Measuring Performance

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Measuring Performance
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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

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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.

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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

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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

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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.

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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)

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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

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Now Answer the following questions in your jotter
..
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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

• How many gigabytes of memory would a 40 bit
  address bus be able to address if the data bus
  length was
• 8 bits
• 16 bits?

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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
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• 5. Abdul has a 2.5GHz PowerPC and Sarah has a 2.7
  GHz CompaqPC. Sarah says her computer is faster
  than Abduls because it has a higher clock rate.
• Do you think this is true?
• Describe a test that could be done to see if she
  is correct.