Prime95 is basically a Mersenne prime number discovery program. It's a great example of Distributed Computing, but it's most loved by overclockers for its powerful system stress-testing and benchmarking abilities. It can torture-test your CPU to produce its maximum heat or spit out any errors due to excessive overclocking. Also, using the blend test, it can consume all your physical memory and run error-checking tests on your modules to ensure their quality. However, right now, we're mostly interested in it for its benchmarking capabilities.
Note here that less is better. Having said that, the Intel well and truly reigns supreme in this test as one can see from the above graph.