Higher Computing

Computer Systems

3. Computer Performance

Clock Speed

• When comparing one computer's performance against another, one of the main criteria is the clock speed of the processor.

• The clock is controlled by an internal crystal and pulses at a regular rate.

• All activities start on the pulse of the clock.• Cycle time- the time between pulses.• Not reliable – some instructions take several cycles

and some computers can perform several tasks per cycle.

Other ways of measuring System Performance

• MIPS – millions of instructions per second.

• FLOPS – floating point operations per second (measure of calculating speed)

• GOPS – giga operations per second – a measure of multimedia performance.

• Benchmarks – standard set of tasks

MIPS

• Millions of Instructions Per Second

• These are machine code (low level) instructions.

• The types of instructions are not specified.

• Only useful if all test conditions are the same.

MIPS continued• Wikipedia says:

– Critics of the term refer to it as "Meaningless Indication of Processor Speed“– MIPS are certainly not comparable between CPU architectures.– See table for MIPS performance down the years.

• Remember: All improvements have a cost. When deciding how to improve a system the ratio of cost to best performance will always be considered.

FLOPS

• Floating Point Operations Per Second

• Measures arithmetical calculation speed.

• More reliable than MIPS.

• A supercomputer is defined as a computer that operates at 1 or more gigaFLOPS.

Application-based Tests

• Used to test both system and software performance.

• Allows comparison of different systems by using benchmark tests. e.g. sort 300,000 database records.

• See Scholar 3.2.2

• Examples of benchmark tests include:– Dhrystone Test

– Whetstone Test

– MemStone Test.

• Investigate these tests.

Application-based Tests

• When reviewing products, reviews use benchmark tests.

• See http://www.pcpro.co.uk/labs/

Measures of Processor Speed (copy)

• Clock Speed – unreliable

• MIPS – millions of instructions per second

• FLOPS – Floating Point Operations Per Second

• Benchmark – set of standard tests

Factors Affecting System Performance

Factors Effecting Performance

• Data Bus Width– The wider the data bus, the greater the word

size.– Investigate data bus widths on current PCs.– What effect would adding a wire have to the

data bus?

Factors Effecting Performance

• Use of Cache Memory– Cache is connected to the processor by its own

bus that is wider than the data bus.– Cache memory is made up of SRAM.

Computer Performance

• An interface speeds up computer performance. It is used to make the link between the fast processor and a slow peripheral.

• Parallel data transmission built into a computer will use at least 8 lines to transmit data.

• Serial data transmission would use one line to transmit data.

• Parallel data transmission is faster than serial.

Interfaces (copy)

• An interface compensates for differences in operating characteristics between a computer and a peripheral.

Factors Effecting Performance

• Data Transfer to and from Peripherals– Depends on the interface.

– Task:• Find the data transfer rates of the following interfaces:

– USB1

– USB2

– Firewire

– Note: using a faster interface with a peripheral designed for an older one will not improve performance.

Factors Effecting Performance

• Add more Main Memory– Virtual Memory – use of fast access backing storage to

behave like RAM. Much slower than using actual RAM.– Most computers do not come with as much memory as

it is possible to address. This is because:• Costs of computer manufacture is reduced• Applications rarely need the maximum amount of RAM to run.• Some memory locations that need to be addressed are in ROM.

Factors Effecting Performance

• Increase VRAM• Increase Clock Speed• Add more processors

– This allows for parallel processing where several processors share tasks enabling them to be completed quicker.

• Increase address bus width.– What effect does this have on total addressable

memory?

Factors Affecting System Performance (Copy)• Increase data bus• Use cache memory (shorter fetch-execute)• Use an interface• Parallel data transmission• Add memory• Use virtual memory• Increase video RAM (VRAM)• etc

Current Trends in Hardware

• TASK:– Compare the clock speeds, RAM size and

backing storage capacity of similarly priced PC’s from now and from 1, 2 and 5 years ago.

– Use PC Pro magazines.– Complete questions on question sheet.