64 bit - 64-bit Performance Advantages

Question

What is the source of the performance advantage 64-bit applications have over 32-bit applications? I'm assuming there is a performance advantage because programs like WinRAR advertise it.

Also, can we get these performance advantages simply by switching to a 64-bit compiler, or are there any changes in code that need to be made?

Answers related to both, unmanaged and managed code, are welcome.

Answer 1

The x64 architecture doubles the number of general purpose registers available in the x86 architecture, so that compilers are able to keep more data in (very fast) CPU registers rather than in (relatively slow) RAM.