The CPU is possibly one of the most important, and misunderstood parts of a modern computer system. There are several different types of processor available on the market today, the most common being made by Intel and AMD.
Intel makes the Pentium 4, Core 2, Core 2 Quad and Celeron processors. They are the larger of the two companies and due to their well-oiled marketing department they have become more of a household name than AMD. The Intel Core 2 is increasingly becoming the most common high end processor found today in computers. The Pentium 4 is still available but is slowly being phased out, while the Celeron is their budget processor. The AMD is available in the Athlon or Sempron. The Athlon is the high end processor, available in various guises, including the X64 X2 dual core and Phenom X4 quad core processor, whilst the sempron is the budget processor which is loosely based on the older Athlon XP range. The XP processors were considered only a few years ago to be the best available for gamers and people wishing to “overclock” their PC’s.
AMD and Intel processors perform very similarly, with the AMD processors being generally cheaper than their Intel counterparts, making AMD the preferred choice for many people. This is in most part due to the Intel being more widely available in retail packaging. In choosing between the budget processors (Sempron and Celeron), and the top-end processors the main consideration should be what sort of things you want to do with the system. Intensive applications (Games, video editing, 3D rendering, etc) are much more suited to the top-end processors. Simpler applications, such as email, internet access and word processing require much less processing power, making the cheaper budget processors a much better choice.
The speed of a processor is measured in Megahertz (MHz), or Gigahertz (GHz). 1000MHz is equal to 1GHz. In general, the more megahertz the better for intensive applications. Intel and AMD use a rating-system that gives an equivalent megahertz rating, this can sometimes be confusing to the layperson when trying to estimate how powerful the processor is.
Given the speeds at which modern processors are capable of operating, the processor is often a good place to compromise, in order to keep costs down. Virtually any of the modern, top-end processors are capable of all but the most demanding of tasks. When looking to choose a system, stop and think, do I really “need” 4GHz for what I want to do, when a 3GHz will do? In many cases the answer is NO, and your money would be better spent on other components, such as a good graphics card, or a better/larger monitor.