[opensource-dev] 64 bit pointers

[Argent Stonecutter]

On 2010-10-24, at 15:44, Boroondas Gupte wrote:
>> If so the 32-bit app will usually run faster.  They do in the HP-UX and Solaris environments, anyway.
> I've never worked with these two UNIX systems, but I don't think this is generally true. On Linux and Windows, a properly optimized 64-bit binary should usually perform the same or better than a (also optimized) 32-bit binary build from the same source. In a lot of     cases the difference will not be significant, but there are exceptions: Especially for number-crunching (e.g. in scientific simulations) at high precision 64-bit binaries often outperform their 32-bit counterparts.

This has nothing to do with the OS. In every environment I know, 32-bit is faster then 64 bit. Every environment but one.

That exception is intel's x86 and amd64 architecture.

That's because in the AMD extensions to the 64 bit architecture, AMD not only extended the instruction set to support 64 bit, but they quadrupled the size of the register file. The biggest problem that the intel architecture had was the tiny register file, so on x86 the 64-bit mode is MUCH MUCH easier to optimize for than the 32 bit mode.