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.

Answer 2

In order to take advantage of the 64 bit architecture of the latest CPU's you have to:

• use a 64 bit CPU and OS
• develop specifically for 64 bits using a 64 bit api - the implementation has to go all the way down to the most basic code working with the CPU registers (normally written in assembler) to take advantage of the extra registers.
• develop an application that will really benefit from the extra registers - WinRAR is an application that will take full advantage of the extra registers because it involves a lot of calculus with complex algorithms. If you instead write an application with very simple algorithms, it will not require extra register address space and it will not work faster on 64 bit
• take also into consideration that when you use a CPU register even if you don't use the the whole address space for a value, it will still take up as much space ( = 64bits).. therefore writing a small application in 64 bit aiming for getting a optimized code will just not work.. that app will take up twice the RAM than if it would be developed under 32 bit and it may be even slower. Programming in 64 bit makes sense for applications using heavy algorithms or that need to allocate huge pieces of memory (4Gb is the limit for a 32bit app).