CPU refers to one of two different things:
- The 'box' part of a computer to which all of the other parts are attached (such as the display screen, keyboard, mouse, printer, scanner, etc.). This part actually houses several different systems.
- The Central Processing Unit aka 'The' chip is an important part of every computer. The CPU is like the brain; its job is to carry out instructions and calculations. Many times CPU's have recognizable names such as: Pentium, Pentium IV, Athalon, Opteron, Itanium, Alpha, 80486, and others.
The CPU is an electronic machine that works on a list of things to do. It reads the list, one item at a time, doing each instruction in order. A list of instructions that a CPU can read is a computer program. A machine that can perform the job of a CPU is often called a Turing machine by mathematicians.
Here are some of the basic things a CPU can do:
- Add two numbers together
- Test to see if one number is larger than another
- Move a number from one place to another
- Get a number from memory
- Jump to another place in the instruction list
Even very complicated programs can be made by combining many simple instructions like these. This is possible because each instruction takes a very small time to happen. Many CPUs today can do more than 1 billion instructions in a single second. In general, the more a CPU can do in a given time, the faster it is. One way to measure a processor's speed is MIPS. FLOPS and CPU clock speed (usually measured in gigahertz) are also ways to measure how much work a processor can do in a certain time. This is what is important to GIMPS.
A CPU is built out of logic gates; it has no moving parts. The CPU of a computer is connected electronically to other parts of the computer, like the video card, or the BIOS. A computer program can control these peripherals by reading or writing numbers to special places in the computer's memory.