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I was reading about WOW 64 here http://en.wikipedia.org/wiki/WOW64

and learnt that its a layer in 64 bit Windows OS to run 32 bit programs.

So can I assume that 32 bit programs run relatively slower on 64 bit OS against when they are natively run in 32 bit OS.

I can see the advantages of memory access of over 4 GB in 64 bit OS. But does this advantage necessarily offset the small overhead added by layer of WOW64 ? Are there any other advantages of 64 bit which offset this.

peterh
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Madhur Ahuja
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1 Answers1

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The main advantage of a 64-bit system is that it allows applications in 64-bit mode, which, in turn, is primarily useful if you need to access more than 4GB memory. If you have that requirement, using a 64-bit system is your only choice. Your application would be using 64-bit code, so WOW64 would not be used, and thus not cause problems.

If you don't really have the requirement to use more than 4GB of memory in a single process, it becomes debatable whether 64-bit Windows is really an improvement. You might need 64-bit Windows if you want to use more than 4GB of main memory at all (although you can also use PAE for that, which has its own disadvantages). Still, on a 64-bit system, you can run 64-bit applications. With AMD64 processors, 64-bit mode might be faster than native 32-bit mode, because the processor has more registers. Whether this slight gain outweighs the slight loss wrt. WOW64 depends on your application mix.

Personally, I think many people install 64-bit Windows because they don't fully understand the consequences of doing so, but feel they are on the safe side (which they may not, due to the lack of drivers).

Martin v. Löwis
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  • Well, for my 32 bit app having 4GB address space rather than 2GB is a significant benefit. Also, 32 bit multi-core apps do tend to run a little faster on 64 bit OS than 32 bit OS, at least for my app that's the case. – David Heffernan Jan 20 '11 at 20:15
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    This doesn't answer the question: would the 32 bit application be slower on 64 bit windows in emulated mode, than it would be on 32 bit OS? How big this overhead would be? Maybe this answer was true in 2010, but now it's clearly not. Most of systems for regular consumers (PC) are 64 bit now and people often have 8GB - 32GB of ram in regular desktop computers. Most of drivers are now primarily available for 64 bit systems. – Petr Mar 15 '15 at 11:12