Central processing unit
From the Simple English Wikipedia, the free encyclopedia that anyone can change
A CPU (Central Processing Unit) is an important part of every computer. It truly is the brain of the computer, since almost everything in the computer must use the CPU in one way or another to get its job done. You can catch a visual glimpse of the CPU doing its thing when the computer is first switched on. If there's no graphical logo screen showing the brand of computer, you can see white text on a black background with what's usually referred to by most people as "gibberish". This gibberish is really just the CPU telling the BIOS to check the motherboard and make sure all the necessary components are in place and working in order to hand the job of booting the computer from the BIOS to the operating system (such as Windows, Mac OS, etc). While this POST (Power On Self Test) is technically run by the BIOS, the BIOS must use the CPU to get its job done. The only way to "watch" what a CPU is doing is to hook up an oscilloscope or other electrical monitoring equipment, since a CPU has no moving parts.
The first version of what could be considered the "modern computer" is generally agreed to be the IBM-XT and XT-like computers released in the mid-80's, most of which had 4- and 8-MHz processors in them. Processor speeds are measured in hertz (Hz). 4 megahertz (MHz) means 4 million times per second. While this may sound like a lot, today's computers have processors that run at 3GHz, which means that they complete 3 billion instructions per second. This large difference in speed means that today's computers run very quickly, but the speed of a processor is not the only factor in how fast a computer runs during daily use. Because the processors are so fast these days, the regular increases in speed have slowed down and are allowing the rest of the components to catch up.
Looking to the future, we may use something similar to what we think of as a CPU, or we may use something that hasn't even been dreamt yet, but one thing is for sure: while the desktop CPU has seen large changes in the past 20 years, these are nothing compared to what the next 20 years will bring. Some people are looking forward to quantum computing as the next logical evolution of the processor.
