The Brains of the Computer
Introduction: At the core of every computer is a device roughly the size of a large postage stamp. This device, known as the central processing unit, or CPU, is the "brain" of the computer; it reads and executes program instructions, performs calculations, and makes decisions. The CPU is responsible for storing and retrieving information on disks and other media. It also handles moving information from one part of the computer to another like a central switching station that directs the flow of traffic throughout the computer system. STEP 1: Integrated Circuits and Transistors In personal computers, the CPU (also known as the microprocessor) consists of a single integrated circuit. An integrated circuit, or IC, is a matrix of transistors and other electrical components embedded in a small slice of silicon. (Transistors are essentially microscopic electronic switches: tiny devices that can be turned on and off.) STEP 2: Where the CPU Lives Like the dozens of other integrated circuits that inhabit your computer, from the outside a CPU chip looks something like a square ceramic bug with little metal legs. These "legs" are designed to fasten the chip to a fiberglass circuit board that sits inside your computer and to carry electrical impulses into and out of the chip. STEP 3: The Chip Inside the ceramic case is the chip itself, a slice of silicon about the size of a fingernail. At first glance, it's hard to imagine how this tiny device can run your entire computer. But under a microscope, the slice of silicon reveals an electronic maze so complex that it resembles an aerial photograph of a city, complete with hundreds of intersecting streets and hundreds of thousands of minuscule houses. Most of the "houses" are transistors, and there are usually somewhere between a hundred thousand and several million of them on a single CPU chip. STEP 4: How Fast Is Your CPU? The type of CPU that a computer contains determines its processing power-how fast it can execute various instructions. These days, most CPUs can execute on the order of millions of instructions per second. The type of CPU also determines the precise repertoire of instructions the computer understands and, therefore, which programs it can run. STEP 5: The System Unit The CPU resides inside a box known as the system unit, along with various support devices and tools for storing information. Just think of the system unit as a container for the CPU. The system unit case-that is, the metal box itself-can either be wider than it is tall, in which case it usually sits on top of your desk, often underneath the screen, or it can be taller than it is wide, in which case it generally sits underneath your desk and is referred to as a tower case.