What some people and I am one of them like to do is overclock our computers to get more speed out of them turning them into a cheap, high-end computer.
If you really do not know what you are doing, be careful as here is why.
Computers are built to work at a certain range, what happens is that the manufacturers of the parts are given minimum specifications, often they exceed these specifications so what some people do is attempt to take advantage of this by trying to get parts to work at a faster rate then the designer of the computer demands. The reason the manufacturer did not do it, is because they had doubts about pushing the computer components that fast.
Now if you want to do something like this, you need to be clever, often it takes a lot of time to get it going and making it stable as the results can be unpredictable although often quite satisfying.
This computer where you see the green arrow processor is being cooled with dry ice. What the overclocker is doing every so often is putting dry ice there to keep the processor cool. To keep a processor running fast, you have to keep it cool.
If you are trying to speed up point of sale software, you will get a speed increase on slow computers but not fast computer as most of the delay on the fast computers is due to harddrives and memory, which cannot be overclocked. The added advantage here is that the slow computer is not worth much anyway.
Finally a warning to anyone thinking of overclocking, it will void the warranty of your computer, and it may wreck your computer. In my experience, people are reluctant to buy any computer that has been overclocked for this reason.