What are the two main differences between 32-bit and 64-bit architecture?

The principle difference is the amount of data that is processed at one time. A 32 bit processor generally processes 32 bit "chunks" of data at any one time. 64 bit, as you probably will guess, processes 64 bit chunks.

Because more data is processed with 64 bit systems, they run faster than 32 bit systems - although not twice as fast as you might expect (or hope!). That's because processing data is only one thing that a processor has to do - it also makes decisions, moves information around, control peripherals and so on. So 64 bit systems run around 10-15% faster than 32 bit ones.