Benchmark is a procedure to find the perfomance ratings of a particular system in terms of factors like multithreading, memory data transfer, graphics power, HDD speed, overall system perfomance etc. There are many benchmarking utilities for different purposes. It can also be used to find any fault in products like ram or gcard. You can compare your benchmark results with the one from another system to compare perfomance in each segment.
For general benchmarks:
PC Mark from Futuremark
Everest(U can do all benchmarks individually)
Sisoft Sandra("""")
etc
For memory benchmarks
mem test 86
everest mem benchmark
etc
For graphics benchmarks
3D Mark 2003(for cards with Dx 8.0 support)
3D Mark 2005( Geforce FX nd cards supporting upto shader model 2.0)
3D Mark 2006(Geforce 6,7 and ATi X1000 series with SM3.0)
For optical Drive benchmarks
Nero CD/DVD speed(best one)
For HDD benchs
Use Everest and Sisoft Sandra.
For Multithreaded CPU Benchmarks
PC Mark 2005 or 6
3D Marks's CPU arithemetic score.
Most of these softwares specified are either freeware of shareware(U can use many limited features) or even demo can be used to benchmarks
Before starting benchmarks like memory test, make sure your memory sticks are perfectly healthy and a weak module might get damaged as during benchmarks each of the system components undergo maximum stress. Its of no harm to peripherals like CPU, mobo, HDD, Gcard etc but use caution for memory especially is your ram/memory is overclocked.
PLEASE rep if helpful