There are two competing companies when it comes to CPUs: Intel and AMD. (There are other manufacturers, but not for consumer systems.)
As of August 2010, there are roughly two types of AMD CPUs:
- Athlon II
- Phenom II
Both come only in 64-bit modes and both usually have multiple cores. Athlons tend to be a little cheaper and weaker, while Phenoms seem to be slightly more expensive but more powerful.
Pay attention to the following statistics:
- Speed in GHz: This is how many operations it can do in a second. More GHz means more power, which also means it needs more cooling and may be louder. You generally don't need more GHz nowadays.
- Cache in MB: This is how much memory can be stored on-chip. This is important, because at the speeds that CPUs run, talking to memory takes a very, very long time. The bigger the cache, the faster your computer will run.
- Cores: This is how many CPUs are inside this chips. The more cores, the better, especially if your computer is doing more than one thing at once. Each core is running in parallel with every other core.
- Bus Speed: This is how fast the CPU can communicate with the rest of the system. The bigger the better. The units are either in MHZ or MT/s. Each MT/s = 2 MHz, so 2000MHz is 4000 MT/s.
- Fan included: Generally, you want to get the fan with the chip since you'll save a lot of money.
- Power Consumption in Watts: All the power consumed is turned into heat, which must be removed from the system. The lower, the quieter your system will be and the less energy it will use. 65W seems to be a really low number.
Matching with Motherboards
First, make sure the socket matches the motherboard socket. The socket is something like 'AM2', 'AM2+' or 'AM3'.
Next, make sure that the bus speed of the motherboard meets or exceeds the bus speed of the chip. If you get a slow motherboard, you're wasting money on the chip, and vice-versa.