Measuring System Performance The speed of a computer is often referred to as THROUGHPUT. This is very difficult to measure. It can be done with Measures of Processor speed: Clock Speed MIPS: Millions of Instructions per Second FLOPS: Floating Point calculations Measures of Overall Computer Performance APPLICATION TESTS a test involving running programs.

Measuring System Performance Clock Speed Can only be sure to work for PCs with the same make & model of processor. BUT Even when two machines have the same processor, one might have faster interfaces or more RAM etc.

So clock speed doesn’t take account of other factors like: Size of data bus Having enough RAM Speed of Interfaces

Measuring System Performance MIPS Millions of Instructions Per Second A 4 MIPS computer seems to be a lot faster than one rated at 2.5 MIPS. Sometimes referred to as : “Meaningless Indication of Processor Speed",

However MIPS only works if the processors have the same instruction set. Different types of processor have different types of instructions, some instructions do a lot of things, some very little.

Measuring System Performance FLOPS Floating Point Operations Per Second Compares computers for scientific calculations, but doesn’t tell you how they rate for other functions. Humans operate at milliFLOPS Calculator 10 FLOPS A Pentium IV at 3GigaFLOPS Playstation 3 will be 2 TeraFLOPS The fastest computer in the world is 71TeraFLOPS

FLOPS are generally best for comparing processors. It only tells you about one aspect, but processors are performing these calculations all the time. Not just for calculations like Spreadsheets, but for graphics, Windows operations, compression etc.

Measuring System Performance APPLICATION TESTS Running programs to test how fast a computer is. Each benchmark measures how good a computer is at that test. By running various benchmarks you get a good indicator of a computer’s overall performance.

Benchmarks treat the PC like a ‘black box’. You have no idea how fast a processor it has, how much RAM etc. But you can compare it to other computers at how good it is at: Spreadsheets Photoshop Doom Etc.

The factors that affect system performance are: Data Bus width Memory Clock speed Buffers

DATA BUS The larger the data bus, the more bits that can be transferred between processor and memory in one go. This is called the WORD size. A 64 bit computer will be much faster than a 32 bit computer because twice as much data is going back and forward each time. Click picture to play video

ADDRESS BUS The wider the address bus the more memory locations the processor can address. THIS DOES NOT DIRECTLY AFFECT COMPUTER PERFORMANCE AT ALL. However you must ENOUGH memory, and generally the more the better. If a computer runs out of RAM it uses the hard disk as virtual memory. This is very, very slow. Adding memory will dramatically improve the performance in this case.

CACHE MEMORY Cache stores commonly used instructions and data. More cache improves system performance because if the processor can use it rather than ordinary RAM then reading and writing to memory will be much faster. Using cache saves having to access slow RAM.

CLOCK SPEED The clock speed has the biggest effect on system performance. Each time there is a clock pulse, the processor can go to the next step in the fetch-execute cycle. So a Pentium 2 Ghz is theoretically twice as fast as a Pentum 1Ghz. (however things are never that simple, bus speed, RAM access, data bus etc. all affect the speed) Click picture to play video

BUFFERS Storage provided by a peripheral or its interface is called a buffer. These can improve system performance because the processor can send all the data intended for a slow peripheral to its buffer and so can get on with something else instead of waiting for it. If the buffer is not large enough to take all the data then the processor will have to wait until it can, slowing down the computer.

INTERFACES Interfaces have a speed. When USB came out, version 1.1 had a transfer speed of 1.5 MBps. Now USB 2.0 has a speed of 60 MBps This will improve computer performance as data transfers a lot quicker between processor and peripheral. More on Interfaces in Unit3.

Enhancements to performance: Wider data bus Sufficient memory (wide enough address bus) More cache Faster Interfaces Faster processors (clock speed) Buffers