Without a central processing unit, your computer can't compute. The CPU -- a piece of silicon -- performs the general purpose calculations for the computer. For most of the personal computer era, the rule for processor speed was simple: always get the fastest processor your budget could manage. When multiple-core CPUs hit the consumer market, that advice shifted. It is now easy to buy a processor that sits idle for hundreds or thousands of clock cycles, waiting for you to do something. Although the processor is still important, other computer parts can be more important to the overall responsiveness of the machine.
Computer usage ranges from driving multiple large, high-definition screens for a video game down to surfing the Web and playing Facebook games. In general, the more demand you put on your computer, the higher the performance you need. The downside of high performance is higher energy usage. High energy use translates into higher operating temperatures and reduced battery life for laptops. Both Intel and AMD have processors designed to minimize energy use while providing enough computational power to handle basic Web surfing. For Intel, this is their Atom line of processors and, for AMD, it's their Fusion line of processors.
Clock Speed, Cores and Threads
Processors are rated with a clock speed. One Hertz is an operation per second. A kilohertz is a thousand operations per second. A gigahertz is a billion operations per second. Higher clock speeds generally translate into more performance. Different processor architectures make it difficult to directly compare clock speeds; this is why computer magazines run real world benchmarks that show how long it takes different models to perform the same tasks. Nearly every modern processor now has two or more computing cores. Modern operating will put different programs onto different cores if they aren't likely to share data with each other. Beyond that level of subdivision, computing tasks are broken down into threads, which can be executed by a core in parallel; this is sometimes called "hyperthreading," "out of order execution" or "branch prediction." Most modern processors are, effectively, Siamese twins.
Multiple Cores and Performance Gains
It's natural to assume that doubling the number of cores on your computer will double the effective speed. The reality is that the second core added to a machine adds somewhere between 50 to 70 percent of the computational power of a single core machine; the excess is taken up in overhead managing the task split, and not all tasks are going to be balanced evenly between both cores. Each additional core past the second one on a processor will typically add another 25 to 40 percent boost in net effective computational power. Adding more cores doesn't always translate into visible performance, but it does reduce the number of times your computer slows down while it is running a large number of programs. Again, how you use the computer determines how much processor you need.
Other Factors Influencing System Performance
Your computer is more than just the processor. The graphics processing unit is just as important as your CPU for gaming, and arguably more so. In terms of how well the computer responds to general use, most users would be better served by getting a slower processor and using the money saved on getting a hybrid or solid state hard drive; both of those technologies attempt to speed up the slowest bottleneck on the computer, which is getting data from disk. Adding more RAM can give a more noticeable speed boost than upgrading the processor.
- Thinkstock Images/Comstock/Getty Images