I know the advantages of 64 bit over 32 bit, but except for compatibility, are there any advantages of 32 bit applications over 64 bit ones? Are 32 bit apps faster?

CodePudding user response：

In short, no. To be more accurate, it might theoretically be the case for some processors, but none that I'm aware of.

The only other difference that comes to my mind is that 32-bit instuctions are generally smaller (due to not having a REX prefix, at least), so you might save some space this way, but it probably doesn't outweight the benefits of x64. Considering that instructions unique to x64 also tend to have higher impact, i.e. manipulating more data at once, the code might even turn out to be more compact in x64. And, for the same reason, x32 is generally slower. So no, x32 doesn't have any real advantages over x64, other than compatibility.

CodePudding user response：

There's one big advantage: 32-bit applications use significantly less memory (precisely because pointers are smaller). Not everything is a pointer, e.g. strings and numbers don't change their size, so the effective difference is not 2x. I happen to know about JavaScript engines specifically, where the 64-bit version typically uses around 50% more memory for the same workload than the 32-bit version of the same engine.

V8 has recently addressed this by implementing "pointer compression" in its 64-bit version. In theory, any C/C app could do the same thing, but it's a big engineering effort.

That said, this generally isn't a reason not to move to 64-bit, as other benefits (more registers, more address space) typically outweigh this drawback. But it does mean that if you're targeting devices/machines with less than 4GiB memory anyway, you might want to stick with 32-bit builds, if memory consumption is a concern.

(Performance, in my experience, is a mixed bag: smaller code and smaller data mean better cache utilization on 32-bit; OTOH having more and wider registers on 64-bit can save instructions there. In rare extreme cases, a 64-bit app can process twice as much data in the same time; most of the time the difference will only be in the range 1-5%, and can go in either direction: sometimes a 32-bit build is indeed a little faster than a 64-bit build; it really depends on what the app is doing.)