When you're buying a new computer of any sort, the most important thing to find out is what sort of processor it has inside.
How can I tell what processor a PC has?
For PCs and laptops, it's almost certain that there's an AMD or Intel processor inside, so look for their branding and logos. Not all processors from the same manufacturer are the same. There a six different types of Intel processor to choose from, and three variations of AMD ones, and performance varies wildly between them all.
Which is better?
Intel processors can be ranked by their brand name: Atom processors are commonly found in low-power netbooks, and aren't as fast as Celeron processors. In turn, Celeron processors aren't as powerful as Pentiums. The most powerful are the Intel Core i3, Core i5 and Core i7 ranges of CPUs (central processing units), in that order.
For AMD, the system is slightly simpler. The Fusion range of processors is designed to be cost effective and low power, and you'll often see them in netbooks. In laptops and desktops, meanwhile, Athlon branded CPUs aren't as quick or capable as Phenom II branded ones.
How do you compare them?
The easiest way to compare processors is by 'clock' speed, or the number of computational cycles per second they are capable of. This is usually written down in Gigahertz. It's important to understand that you can only really compare clockspeeds within a particular range of CPUs, though. A 3GHz Intel Celeron processor, for example, isn't as quick as a 2GHz Core i7.
Are there any other considerations?
Processors today are so powerful that there's really no need to buy the fastest possible unless you're editing large amounts of HD video or playing games. Buying a low power CPU that can extend battery life is much more useful for a laptop or a tablet, and if you're watching videos, reading email and surfing the web, you won't notice the difference.
How many cores do you need?
Nearly all new CPUs are 'dual core' processors. That means they have two identical processing units in the same chip, and can do double the work of an older single core CPU. More advanced, and expensive, processors can contain four, six or eight cores for even better performance.
What about ARM?
Mobile phones and tablets use ultra-low power processors, which can extend battery life in these highly portable devices. These CPUs might be made by Samsung, NVIDIA, Apple, Qualcomm or others, using a basic design by the British company ARM. ARM-based chips aren't as powerful as AMD or Intel ones, but use very little power and are highly cost effective to produce.
Processor - the Central Processing Unit, more commonly known as the CPU or processor, is the most important chip in your PC. It does all the number crunching and assigns tasks to other parts of the system. The more powerful this is, the faster your PC will be.
Hybrid processor - some newer chips, like Intel's second generation Core processors or AMD's Fusion range, also contain a graphics processor next to the traditional CPU. These aren't as good for graphically intensive tasks, like gaming, as having a separate video card, but they are very power efficient and can extend the battery life of a laptop enormously.
Socket - this is the physical port on the motherboard that the processor is put into. In desktop PCs, you might be able to upgrade a processor at a later date, providing the socket size is compatible with your new chip.
Cache memory - you may see a processor described by its cache memory. This is a small amount of high-speed memory built into the chip used to increase performance. Larger amounts of cache memory are better, but don't confuse it with the computer's data storage known as RAM.