Can 32-bit software utilise more memory in 64-bit Windows?

By ulrichburke ·
Dear Anyone. Need to use Windows XP for an old 32-bit program I've got - but just discovered there's a 64-bit version of XP I'd never heard of! I've got 6-gig of Ram. If I install the 64-bit XP, would the 32-bit program be able to utilise all 6-gigs (not counting what Windows is using, of course!) Or can it still only use 4 gigs?

Yours puzzledly, Chris!
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32-bit software utilise more memory in 64-bit Windows

by aravindmuniraj In reply to Can 32-bit software utili ...

When an x86_64 processor executes 32-bit code it is effectively running in i686 mode. This is all achieved in hardware so there is no performance penalty.

A user-space 32-bit program will be executed in "32 bit mode" whether the operating system is 32 bits or 64 bits so the behavior should be identical.

The only potential drawback is that the program might need to dynamically link to some 32-bit libraries which are not installed by default on the 64-bit OS. That sort of scenario is more common on Linux where it is much more common for programs to dynamically link to external libraries; the only example I can think of on Windows is if the program needs the Visual C++ runtime library then you would have to install the 32-bit version of that (possibly alongside the 64-bit version, if another program needed that). So in short you might have to install more stuff with a 64 bit set up.

Also the actual OS might consume more memory on a 64 bit setup, however one drawback of 32-bit system is that your entire system memory size is limited to 4GB (or practically about 3.5 GB due to some memory space being mapped to hardware).

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