My computer is a Dell Dimension E521, and It has a AMD 64 Athton Duo processor in it. What Processor can I upgrade to? I need something really fast. Thanks in advance.
Service tag code is GTLX0d1.
Most of the time it's not worth upgrading the CPU, if your computer came with a single core sempron cpu (the equivalent of a intel celeron) it would be worth it to upgrade to an Athlon 64 X2 CPU, however, your only option for upgrade (with the 939-pin CPU socket, which is what you probably have) is pretty much just faster Athlon 64 X2 cpus so it's probably not worth the money for the minimal performance enhancement.
Also, what specific model of CPU do you have (look in Control Panel --> system )? This could give more info, if it's truly worth it/not worth it to upgrade.