1.4 - Computer Performance

The faster a CPU can process data and instructions, the faster programs will run, tasks will be completed quicker and the overall running of the computer will be smoother.

There are three key factors that affect the performance of the computer and especially the performance of the CPU:


Cache Memory

As to be explained in Primary Storage next, cache memory is a type of storage that can be accessed by the CPU extremely quickly (because it is so close to, or even within, the CPU).

Cache memory is used to store data that is frequently accessed and it can be accessed faster than other primary memory such as RAM.  Therefore the more cache memory in a computer system, generally the better the performance will be.

However, cache memory is very expensive so most computers only have a small amount.


Clock Speed

The speed at which a processor operates is called the clock speed. The faster the clock speed, the faster  the computer is able to run the fetch-decode-execute cycle and therefore process more instructions.

The speed of the processor is measured in Gigahertz (GHz). One clock tick per second would be measured as  1 Hz. A typical modern day CPU might run at a speed of 3.5 GHZ, equivalent to 3.5 billion clock ticks.

The clock speed can sometimes be changed to run faster than its original design (known as overclocking). This uses more energy and produces more heat which can damage the CPU and shorten its lifespan if not cooled sufficiently. 

Other computer systems, especially mobile devices, intentionally set the clock speed of the CPU lower than its original design. This results in less power consumption, less heat being produced and will therefore increase the battery life of the device. This is called underclocking.

Some devices can change their own clock speed dynamically. For example, when your computer is idle, the clock speed may be set at a lower rate than if you were running a CPU intensive program, such as a computer game.


Number of Cores

A core is the term used to describe the processing components within the CPU (control unit, ALU, registers and internal memory). Multi-core processors therefore have many processing components within the same CPU.

A single core processor executes each instruction at a time whilst a multi-core processor can perform more than one operation simultaneously.

In a single-core CPU each instruction is processed one after the other, whereas in a dual-core CPU, two instructions may be processed at the same time. In theory, a dual-core CPU should be able to process instructions twice as fast as a single-core CPU. However, this isn’t always the case, as sometimes Instruction 2 may need the result of Instruction 1 before it can be processed.

In general, a computer running many programs at the same time will run faster on a multi-core processor than on a single‐core processor.

Questo's Corner

Cache Memory:

a. What is cache memory?

b. Explain why more cache memory generally means a better performance.

Clock Speed:

a. What is clock speed measured in? What is an average modern clock speed?

b. What is meant by overclocking and underclocking?

c. Explain why a higher clock speed generally means a better performance.

Number of Cores:

a. What is a multi-core processor?

b. Explain why a CPU with more cores generally means a better performance.

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