How+do+computers+work

**How do computers work?**
A computer essentially does one thing: it "computes." In other words, computers work with numbers and do math. We are able to use computers to do a lot more than just math because programs have been written to hide the math behind the scenes. For example, when you are in a word processing program, every word you type is translated into numbers and stored in memory. For graphics applications like Photoshop, every pixel on screen is also recorded as a numeric value.

Desktop computers (or "microcomputers") became popular with the introduction of the Apple Macintosh in 1984, and since then they have helped to completely redefine the way we use computers. What was unique about the Macintosh was that it had a graphical user interface (GUI or "menu system") and a mouse. Apple stole the GUI concept from IBM, and Microsoft in turn stole the concept from Apple.

At the heart of the computer is the central processing unit (or CPU which does the math). Everything else on a computer is designed to either (1) get information to the processor, or (2) get information from the processor.

**How Processors (CPUs) Work**
The basic operation of most CPUs is to execute a sequence of stored instructions called a program. The program is represented by a series of numbers that are kept in the computer's memory. There are four steps that nearly all CPUs use in their operation: fetch, decode, execute, and writeback.

The first step, fetch, involves retrieving an instruction (which is represented by a sequence of numbers) from program memory. In the decode step, the instruction is broken up into parts to execute. The final step, writeback, simply records the results of the last step to memory. The entire process repeats millions of times a second.

The faster the processor, the faster your computer will run. Processor speed is measured in MHz, so look for higher MHz numbers when purchasing a computer.

How Computer Memory Works
Random access memory (RAM) is the fastest computer memory available. It can quickly send information to and from the processor, or just hold information until the processor needs it again. All information going to and from the processor must go through RAM first. Once a computer is turned off, everything stored in RAM disappears. This is why saving files often is so important.

The more RAM your computer has, the faster it will run because your processor will not need to access the slower hard drive as often. Graphics programs like Photoshop are very memory intensive. For a graphics workstation a minimum of 2 GB or RAM is required. Having 4 GB is helpful.

**How Hard Drives Work**
Every desktop computer in use today contains one or more hard-disk drives. You can even find VCR-type devices and camcorders that use hard disks instead of tapes. Hard disks do one thing well -- they store changing digital information in a relatively permanent form. They give computers the ability to remember things when the power goes out.

Hard disks have a hard platter that holds a magnetic medium (similar to the coating on cassette tapes). The platter spins in a circle similar to a phonograph record. Numerical information (zeros and ones) are recorded and retrieved as the platter spins. Because hard disks are a magnetic medium, placing a magnet near a hard drive will erase the data. The magnetic medium will also wear out in time, so all hard drives will eventually crash. This is why making back-ups of your files is so important.

The larger the hard drive, the more files you can store in your "filing cabinet." When purchasing a graphics workstation, consider purchasing the largest hard drive you can afford as graphics files can be very large in size.

Other Devices
All other devices on a computer can be categorized as either input devices or output devices. Keyboards and scanners are examples of input devices. Printers and speakers are examples of output devices. DVD/CD drives are input devices, but they can also be output devices if they can burn media. Your USB flash drive is another example of an input/output device. Every one of these devices either helps get digital information to the processor or receives digital information from the processor.