Usually, for games the graphic card is the bottleneck. Unless it's chess. Then it's the CPU (processor).
By the way: the 32-bit/64-bit isn't hardware. It's software. But you'll only notice a difference (in certain situations) if you have more than 4 GB or RAM.
My PC is pretty slow when i play games. which hardware parts need to be replaced?
here are my specs
processor: AMD Athlon(tm) 64 X2 Dual Core Processor 4400+ 2.37 GHz
Installed memory (RAM): 3,00 GB
System type: 32 bitsystem
I am pretty new to the hardware world I hope you have enough information to judge my pc.