How Do Computer Processors Actually Work?

The power of your processor is the key to your computer's performance. The amazingly rapid leaps that are made each year in processor technology are barely matched in any other industry. Here we look inside the processor.

At the centre of your computer is an incredibly fast processor, made up of millions of tiny transistors. On their own, these transistors work as simple on/off switches which is perfect for a digital computer where data is made up of binary 1s and 0s.

To get the transistors to do useful work, they are designed in complex arrangements made up of several thousands of transistors. The trick is to arrange these transistors into functional blocks. By doing this, chip manufacturers can make a processor understand instructions. Processors typically have an instruction set of several hundred or so instructions, which can be used by almost any type of program, and each of which plays its part in running your software and working on your documents and data.

When you type information into a Word document, you see it appear almost instantly on the screen. Likewise, when you type a sum into an Excel spreadsheet, you see the result appear when you press the [Enter] key. The PC's processor (usually an AMD or Intel chip) knows nothing about how Word or Excel actually works. These programs are written in a code that is understood by the processor, thus enabling Word and Excel to translate your actions and commands into a large number of simple instructions, which are part of the processor's instruction set, so that the processor can then carry them out.

While your software, Windows or Word, for example is running, the functional blocks inside the processor work together: one part fetches instructions and data from memory on the motherboard; others execute the instructions and store the results inside the processor.

You can think of the processor as being arranged rather like a factory. Central to the processor are the machines (instruction execution units) that do the work. Equally important, however, is the delivery of raw materials (data and instructions) to the machines at the right time and the removal of finished product (results) so that the next instruction can be executed. This system is built into the processor and defines its blocks and the way they are organized. Some blocks are highly specialized to enable particular operations to be carried out at maximum speed: for example, one is dedicated to carry out complex mathematical operations.

There are three main groups of functions inside the processor: fetching, storing and executing.

To start, instructions must be fetched from memory. First, the cache (a small, but very fast, amount of memory inside the processor) is checked to see if it contains this information. If it doesn't, the processor must fetch it from the memory on the motherboard.

Data is also fetched in a similar process. The data cache is checked and data to be worked on passed on to the chip's storage registers, awaiting an instruction.

Instruction execution means the instructions pass to the decoder, which breaks up any complex instructions into a series of simpler ones. These then travel on to the execution units that actually carry out the instruction. There are two types of instruction execution units: integer units and the floating point unit (FPU). Integer units can handle many instructions easily, but they are very inefficient at some type of calculation, particularly those that involve numbers with decimal points. These are passed to the floating point unit instead, which is an area of the processor that is designed exclusively to calculate complex mathematical operations.

The instructions are then sent to the processor's storage registers where any necessary data is stored. Now the instructions actually operate on the data: the clock ticks and the results are stored once more in the processor's registers. The whole process runs as a pipeline so the next instruction is right behind and ready for execution, having been fetched from the memory.

While a factory might speed up and slow down, according to the time of day and/or demands of work, the processor works at a constant pace, its speed governed by the computer's internal clock. The more ticks per second there are, the faster the instructions are executed.

There are several stages to an instruction's execution. With each clock tick, the processor moves on one step. The clocks, even those that are employed in home computers, tick millions of times a second, and are measured in Megahertz or Gigahertz (2GHz, for instance, indicates two billion ticks per second).

Modern processors can work on several instructions in parallel. This is rather like a team of cooks in a burger restaurant working on different parts of a meal at once. Instead of one person preparing all the parts of a meal in sequence, first the burger, then the chips, next the hot apple pie and finally the drink , several work at once in a parallel pipeline, making the whole meal in much less time.