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CPUs - How do they do it?

© Chris Cruickshank

Have you ever wondered how the central processing unit (CPU) of your computer works? If you have - then here is a simplified version of how this is achieved.

The Brain

The CPU is the supposed "brain" of a computer. It is responsible for controlling what each component within a computer does and when it does it. Just as your brain sends instructions to your legs in order for you to walk, the CPU will send instructions to your graphics card to draw something on screen.

Each device will respond to the CPU by carrying out the instructions and then reporting back that the task is complete. In this way, the CPU can "order" the events that need to happen.

For example, when you save a document, the CPU will calculate the file size and instruct the hard disk to store a file of x bytes in size. The hard disk will check that it has sufficient space and inform the CPU that it has. The CPU will then instruct memory to copy the file to the hard disk. Once done, the hard disk will inform the CPU that the file has been saved. The CPU then tells the graphics cards to display a message confirming that the file has been saved. Of course, if there is a problem along the line (such as lack of disk space), the CPU will carry out alternate instructions.

How is this done?

When electricity is passed through a conductive material, the material will oscillate. The diagram below shows a CPU's oscillations.

The frequency of such oscillations is measured in Megahertz where 1 MHz is 1000 cycles. If your PC is a 300 MHz computer then it will oscillate at 300,000 times per second.

A cycle is the time it takes for the top of one peak to reach the next. The CPU comes with a set of instructions that govern what the chip can do. Each of these instructions will require a certain number of cycles in order for the instruction to be carried out. Once the instruction is complete, the next instruction is carried out and so on.

Therefore, the more oscillations that can be achieved in a second of time, the more instructions the CPU can carry out within a second of time and hence, the faster the computer.

There is one major drawback to increasing the oscillations within a CPU. It is a problem experience by any material that oscillates - especially when the oscillation rate is high. That is: heat.

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