For those buying or upgrading a computer, here's what you ought to know about its most important component: the CPU.

The Central Processing Unit, sometimes simply called the processor, is your computer's brain. It manipulates information within the computer and co-ordinates its flow around the different devices that make up the computer. Intel and AMD manufacturer the bulk of CPUs seen in personal computers. Other manufacturers with a small share of the market include VIA and Transmeta. Processors may be classified into four categories: 

. Server processors
. Budget desktop processors
. Performance desktop processors
. Mobile processors

Server processors

Intel Xeon processors and AMD Opteron processors fall into this category. These CPUs are used in corporate servers and will generally never be used in the desktop computers most individuals have.

Budget desktop processors

In this category we have the Celeron series from Intel and the Sempron series from AMD. These processors are more than adequate for normal office work like typing letters, working with accounts, checking email or browsing the Internet. They can even be used to comfortably watch movies or listen to music. The Celerons range in cost from Rs 2,800 to Rs 3,500, while Semprons cost between Rs 2,400 and Rs 3,000.

Performance desktop processors

These are suitable for those who like to play the latest games or those who work on tasks that require a lot of processing power -- for example, image or video editing. AMD offers the Athlon 64 series (Rs 3,500 to Rs 8,000) and the Athlon 64 X2 series (Rs 8,500 to Rs 10,500). Intel has the Pentium 4 series (Rs 4,000 to Rs 6,000), the Pentium 4 D Series (Rs 6,000 to Rs 9,500) and the Core 2 Duo Series (Rs 9,500 to Rs 16,500).

Mobile processors

Used in laptop computers. Examples are the AMD Turion and Intel processors with Centrino technology. These processors are optimised so they do not heat up as much or drain the battery as much as normal processors do.

Picking the right CPU

Several factors are to be considered when deciding on the CPU for your computer. These are, in order of importance, the applications you will be using, the cost (of course), actual architecture of the CPU, and the way the CPU integrates with the rest of the system.               

The 32-bit versus 64-bit debate

The CPU handles data and instructions applied to the data. The data/instructions are transferred to/from the main system memory (generally called RAM) using a pathway known as the data bus. The wider this pathway, the more the data that can be transferred simultaneously. Therefore, 64 bit CPUs can transfer more data at a time to/from the CPU as compared to 32 bit CPUs. This translates to better performance for certain kinds of operations. The AMD 64 series and Intel CPUs with EMT64 technology are examples of 64 bit CPUs.

What's a cache?

The CPU can operate much faster than the main system memory. Hence, all CPUs also have some memory of their own to speed up their operation. This memory is known as cache and is classified as L1/L2/L3 cache. Generally, the greater the cache, the faster the CPU operates.

Does clock speed still matter?

In order to synchronise its operations, the CPU uses a clock. The speed of this clock is measured in GHz. So, you have processors rated at 2.66 GHz, 2.8 GHz, 3 GHz and so on. Earlier, it was true that the higher the clock speed, the faster the processor. However, this no longer holds true, as lower clock speed processors can outperform higher clocked processors due to other architectural differences.

While on the subject of speed, it is also important to note that the processor name doesn't always indicate clock speed. For instance, the AMD Sempron 2600+ gives the performance of a 2.6 GHz processor but actually runs at 1.8 GHz.

Two hands are better than one

In order to speed up the operation of the CPU, manufacturers resort to different strategies. Hyperthreading is one such strategy from Intel. This technology attempts to obtain higher performance from the CPU by allowing instructions to be simultaneously executed. However, you will see performance gains only if you are using the right mix of applications. To use an analogy from the kitchen, if you were preparing soup, you could begin chopping vegetables instead of waiting while the water boils. However, if you were preparing tea, you'd have to wait until the water boiled before doing anything else.

Another strategy involves placing more than one CPU core within a single CPU package. The Core Duo processors from Intel and the Athlon 64 X2 processors from AMD are examples of this. If we go back to our kitchen analogy, two cooks can certainly cook faster than one, provided the kind of dishes they are preparing allows this. In a similar manner, you would obtain performance gains from dual core CPUs depending on the type of applications you are using and your usage pattern.

Working as a team

The CPU is integrated with the rest of your computer via the motherboard. Motherboards may be classified according to the way the CPU fits onto the board. Thus, we have Socket 754, Socket 939, or Socket AM2 motherboards that support AMD processors. Intel processors fit onto Socket LGA 775 or Socket mPGA478 motherboards. The CPU connects to the rest of the devices in your computer via a FSB (Front Side Bus). This ranges in speed from 400 MHz to 1033 MHz. Generally, the faster the FSB speed, the faster the CPU operates.

Cooling down

While performing its various tasks, at full speed, the CPU generates a lot of heat and consumes a lot of power. Therefore, major CPU manufacturers Intel and AMD have introduced technologies -- SpeedStep by Intel, Cool'n'Quiet by AMD -- to help keep the CPU cooler. A cooler CPU benefits you in many ways. It lowers your electricity bill, gives the CPU a longer lifespan, reduces the level of noise and, in laptops, helps conserve battery power.

Now, the next time you have a chat with your hardware consultant, you know exactly what to discuss.