The Blonde's Guide to Computers: Central Processing Unit (CPU)

Written by:  MD Weems • Edited by: Lamar Stonecypher
Updated Aug 28, 2009
• Related Guides: CPU

You know the term. You know it's a major part of your computer system. But just what is a CPU? Well, here is your answer.

And the CPU is....

Anyone who has ever heard of a computer has heard the term CPU. It is a part of just about every conversation about computers, and yet still there are millions of people who really don't know what a CPU is. Well, CPU actually stands for Central Processing Unit, and is basically the machine part of your computer system that allows it to run the computer programs. Now, this is a really broad overview of what a CPU is and does, but in a nutshell – that's it.

The term CPU was actually first used in the 1960's with many of the earlier custom one-of-a-kind computers. Today, we pretty much know the CPU as a mass produced computer system that is only customizable by a few different features. The good thing is, that with the mass production and the competition that it has caused in the computer companies, CPU's have gotten smaller and smaller over the years and are now in some of the digital devices that you probably use every day and don't even realize it. In fact, there are CPU's in cars, cell phones, and even some of your kid's toys right now in the form of microprocessors.

Ok – so you now know a basic background of a CPU. You know what the letters CPU stand for. But, you still aren't all that clear on what they do. Well, have no fear – that part is next.

The basic job of most CPU's is to perform a specific sequence of instructions that are already stored inside of it's memory in the form of a program. The program is made up of millions of numbers in a special series that are all kept in the computer's memory, which is inside the CPU. CPU's have four basic steps when it comes to their operation and how they run their programs: fetch, decode, execute, and writeback. (Yes, that was a little technical and I told you this was a blonde's guide . . . well, let me explain this a little more, don't worry!)

Let's start with fetch. Just like a dog, your CPU knows how to fetch – but not a Frisbee. To a CPU, fetch means that they have to retrieve instructions from the program's memory. When it fetches the instruction, it then pulls it to the front of the “virtual” line so that it can be decoded.

On to the decode step – now that the CPU has fetched the program from it's memory, it uses the instructions in the program to determine what step to take next. The program makes it easy on the CPU by already breaking up the instructions into pieces that can easily be done by other parts of the CPU itself. So, when the CPU decodes the program, it takes the instructions and then fires off the instruction pieces to the different parts of the computer that are needed to perform the program.

Now that the CPU has gotten the program and it has decoded the pieces and fired them off where they need to go, it can now begin to execute the steps in the program. This means that it does what it was told to do (unlike many dogs I know, including mine). There are actually a lot of steps that go into executing a program, but I won't go into all of that now . . .

And the last step is writeback. No, this is not what your mom tells you to do when she sends you a card. This just means that the CPU “writes back” all of the results from the executed program in it's memory. Normally, these results are written in an internal CPU register so when the CPU performs the same process again, it knows what to do.

So, hopefully, you how have a better understanding of what a CPU is and what it actually does for your computer system. Now, you aren't in the dark like most of the computer users in your office!

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