## Beginner’s Guide to Understanding the CPU: How the CPU Works

written by: Ashwin Satyanarayana•edited by: J. F. Amprimoz•updated: 6/6/2009

Have computers been a mystery to you? Did you ever stop to think how is it that the computer is such an efficient machine? Say thanks to the CPU. So how does it work? What makes it tick? How is it that it is able to deliver so much? Read on to learn more:

• slide 1 of 2

### The CPU's Job in a Computer

Computers aren’t any mystery, even though the workings can seem to be complicated. In order to understand how they work, it is important to think of the computer as an assembly of some logical modules (blocks) all of which work together. The explanation forthcoming in this article won’t suffice for your actual understanding of the modern day digital computers, but can at least provide a solid start for you.

Starting at the very basic level, think of how an electric switch works - when you flick on a switch, a bulb goes on and when you flick it the other way around, it goes off. That’s just one switch. Similarly, you could have 10 switches which are all linked an to equal number of outputs (bulbs) through an intermediate device called a controller. The controller then determines which bulb must be switched on depending on which switch you had pressed.

A computer, on a very basic level of understanding, works just like the circuit mentioned above with a group of input switches (keyboard keys, motion sensor inputs, etc) and corresponding output like letters being typed out on screen, a sound alarm, and so on.

An inclusion of two more components or blocks to this particular circuit mentioned above is akin to almost building a very basic computer. All you would need then is a memory and a set of programs that can control the workings of this circuit. The memory would store the calculations and decisions the controller seems to be making during times when the controller has to process information so as to determine which output the input signal must go to. The set of instructions ( also called as programs) instruct the main controller as to how to respond to a series of inputs coming in and what exactly to do with them -- the controller wouldn’t work if it doesn’t know what to do, would it? The controller would also determine whether the output of the controller has to be sent to the output itself or whether it should be stored in memory for further processing.

The amount of memory it can hold, the speed at which the input can be processed and the output can be delivered, as well as the data transfer within these individual blocks are all determined by the capacity of information the machine can handle which would all be in bits (0 and 1). Computers can only comprehend the binary system and an article titled An Introduction to Hardware for Beginners: Bits, Bytes and Beyond “ explains this in detail. You will learn from this article that today’s computers have an 8 bit capability -- which means that we have about 256 various input or output conditions for our use.

Well, it isn’t over yet. The number of bits that can be handled is now growing and we now have approximately 32-bits being processed at a time for Windows XP, for instance. Some of the computers even come with 64-bit processing power which gives enough input/output combinations running into millions.

• slide 2 of 2

#### Understanding the CPU

This series is all about trying to understand the inner workings of a computer -- the CPU and its intricate working mechanisms.