Processor is a heart of computer or we can also say that it is life of computer. Processor means to process something or to do something or to be ready before buying computer we should decide that which processor we are going to buy because everything is dependent in upon processor. if you decide about processor, than only you can buy or look a compatible motherboard because it may happen that the motherboard will not support the processor. Now a days there is competion between two company only one is marker leader INTEL and another is AMD. both the company have given everything for best result. it is also not fix that costing ten thousand processor will give better performance than five thousand . you can use any, either intel or amd if you are taking computer for your basic use. it will be better that take dual core or core2duo because they both consume less electricity and are fast and reliable. you should beware of buying pentium four processor and amd processor ethlonx2 because they are using much more electricity. Processor are mainly comeing in two version one is OEM means Original Eqipment Manufacture and other is Retail. price of retail is less than retail because while purchasing retail you will get any additional software for free and other is you will get cooler fan in retail processor and other main thing to focus are form any where you buy a processor that don't matter but there should have a cooler fan. because it cools the processor. if there will not be cooler fan than after sometime your processor will be heated and it will stop working and you will get massage that "computer was previosly shut down due to overheat or thermal so be careful. some times it may happen that your cooler fan is running computer is being shutdown and giving same massage at that time you should clean your cooler fan or it will be better that you change the fan.