The CPU

The CPU (Central Processing Unit) is the "brain" of any computer. It is the part that does all the calculations, or "thinking." It takes all the data and processes it to give you the results that you see on your computer.

Two companies make most CPUs: Intel and AMD. AMD makes the Sempron, Turion, Athlon, and Opteron chips. Intel makes the Celeron, Centrino, Pentium, Core Solo/Duo, and Xeon chips.

It is difficult to compare CPUs, because there are so many different parts and qualities that must be compared. Some CPUs will be faster in some ways, and slower in other ways. If you are comparing two CPUs in the same family (for example, a Celeron at 1.8 GHz vs. a Celeron at 2.0 GHz), then comparisons can be made fairly clearly--but if you compare two different CPUs (for example, a Celeon and a Turion), it becomes much more difficult.

Generally, CPUs are rated on their general speed, but in notebook computers, power usage is also important.

In addition, the CPU is only one point of many when you determine the speed of a computer. To get an overall ideo of the speed of a computer, you must consider:

• CPU type: Celeron, Turion, Pentium, Athlon, etc.
• Clock speed: how many gigahertz, or "GHz"
• Multicore: how many cores
• Multiprocessor: how many CPUs
• Cache type and amount
• Bus speed
• Amount of RAM

CPU Type

Here is a chart of many of the CPUs being used today:

In general, CPUs at the top are slower, and CPUs at the bottom are faster.

Clock Speed

"Clock speed" refers to how "fast" the CPU "runs." Each chip has a clock speed measured in Gigahertz (GHz), which measure how many calculations per second are performed in the CPU. For example. Today you can buy a Pentium 4 computer running at 3.6 GHz, for example, or an iMac desktop running at 2.0 GHz.

The important thing to remember about GHz is that it is NOT a good way to compare the speed of different computers. If you compare a 3.2 GHz Pentium 4 and a 3.6 GHz Pentium 4, that is a good comparison--the 3.6 GHz model is faster. However, if you compare a 3.6 GHz Pentium 4 and a 2.0 GHz Core Duo, the GHz number comparison is not correct. The two chips have very different designs, and even though the GHz for one chip might be lower, it might be a more efficient chip with a better design, and might do things faster than the higher-GHz chip. In this case, the G5 is a faster CPU even when it has lower GHz numbers.

There are some other CPU features which affect speed:

Multiprocessor

This means that there are more than one CPU in a computer. Having two CPUs does not double the speed, but it does increase speed by perhaps 60% or so. One computer can have two or more CPUs. "Supercomputers" are usually giant computers with thousands of CPUs working together.

Multicore

This is a new feature. It means there is kind of like a multiple CPU in one chip. It is like a multi-processor, but with only one CPU chip. A CPU with two cores is called "dual core," a computer with four cores would be called a "quad core."

Cache

Cache can be very important. Cache is a way to make the CPU much more efficient. L2 cache (on the CPU) is best, and L3 cache (next to the CPU) is still good. 512KB of L2 cache is good, but 1MB is best.

Bus

Also called the "frontside bus." This is the speed at which data is exchanged between the CPU and the RAM / memory. A faster bus means a more efficient and faster CPU. If a Bus' speed is half of the CPU, that is considered fast.

RAM

RAM will be described more on the next page, but it can also affect your computer's speed. If you have too little RAM, your computer might run out of memory, and slow down a lot.

So you can see that there are many different points that can make a CPU faster or slower. For example, the Celeron chip has less cache, a slower bus, and no multi-core or processor features. That's why it can be cheaper.

BUT--keep in mind that you don't always need speed! If you just want to do Internet, email and word processing, a Celeron will do fine. But if you use special, complex software, for example, high-power gaming, movie editing and creation, or computer animation, you may need a faster CPU.