| Section: |
The heart of a computer is a device referred to as the Central Processing Unit (Often abbreviated CPU). The CPU is the physical device where all the fancy processing we talked about in the essentials of computing happens. Every other device attached to a computer system eventually sends information to or receives information from the CPU. The basic kinds of instructions (like the add, store, jump instructions we played with earlier) are built into the CPU. The characteristics of the CPU determine what kind of computer you have.
There are two major types of processors being used in home computers today. Macintosh computers are based on a family of CPUs created by Motorola. IBM compatibles are based on a family of CPUs made by Intel. These different CPU flavors have completely different sets of instructions that they read at the simplest level. A program written to run on a computer based on the Motorola CPU will not run on a computer that uses an Intel chip. Each of these families of processors has a number of models available. The latest processor is almost always much faster than its predecessors, and more expensive. In the Intel world, for example, we have had the 8086, the 80286, the 80386, the 80486, and the 80586. Computer sales types refer to these processors as: 8086, '286, '386, '486, and Pentium processors)
Each of these processors has been roughly twice the speed of its immediate predecessor.
A cpu also has a speed rating based on millions of cycles a second. One million cycles in a second is referred to as a megahertz. Megahertz is usually abbreviated Mhz. In general, the larger the megahertz rating, the faster the processor will be. A 100 Mhz Pentium will be faster than a 66 Mhz Pentium. This rating system is only accurate when you are comparing computers with the same type and generation of cpu. A 25 Mhz 486 is faster than a 33Mhz 386(!)
Since the CPU determines everything else about a computer, it is obviously pretty important. It would be possible to buy a computer and then learn that all the programs you want are written for different CPUs. To avoid this situation, you need to carefully think about what you want from your computer. Visit friends who have computers, look around in the stores, and think about what you really want your computer to do. Go to a software store and look at the programs on the shelves. They will almost always have a little sticker on the box explaining what kind of processor you need to run that particular program. If you see ten programs that you might purchase some day, and eight of them require a 486 or higher chip, an IBM compatible with a 486 or Pentium chip is probably the machine for you. If you really like the interface on Macintosh computers, and don't want to learn anything else, that might be your computer. After you have chosen the type of cpu, you will need to choose a speed. The faster chips are more expensive. Again, look at the software you will want to run. If you can get by with a computer running at 33Mhz, why buy anything faster? Certainly you have more options with a faster cpu, but think about what you will use the computer for. If you will be playing games or doing other graphics - intensive work, a high speed CPU is very important. If most of your time is spent with word processing, the speed is not such a factor. While using word processing programs, even the slowest computers spend most of their time sitting and waiting for the user to type in a character. A very slow computer by today's standards might cycle 33 million times a second. How fast do you type? A general guideline might be to buy as fast a CPU as you can afford, but to worry a little less about speed if you are just using your computer for word processing.