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I just saw these minimum requirements for a game:

Memory: 2GB for 32-bit OS or 4GB for 64-bit OS

Why does the 64bit OS require more RAM than its 32bit counterpart?

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This doesn't mean programs always take twice as much RAM on a 64-bit OS, by the way. –  Thomas Sep 3 '12 at 13:04
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The short answer is yes, 64-bit operating systems almost always require more RAM than corresponding 32-bit operating systems and 64-bit applications often do require a bit more RAM than corresponding 32-bit applications. There are a number of reasons, but the most basic is that pointers take up twice as much space on a 64-bit operating system as they do on a 32-bit operating system.

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I do want to add that the machine doesnt necessarily need more RAM, just the software. –  Keltari Sep 3 '12 at 18:22
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Another component would be "because they can". In the early days of DOS, programs would do massive tricks to stay under tight memory constraints. Under 64 bit, you don't have to. The same program may load more into cache/maps, trading memory for speed. –  Rich Homolka Sep 3 '12 at 18:37
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Good answer, but it's worth remembering that memory is less of an issue on 64-bit systems. The limitations are complicated, but many 32-bit systems can handle only 3 or 4 GB, which is puny in an era when 1GB DIMMs sell for less than ten bucks. On a 64-bit system, you can double or quadruple that for a reasonable cost. –  Isaac Rabinovitch Sep 4 '12 at 5:07
    
For what I know the x32 abi architecture try to exceed this. Here a thought of Donald Knuth. (Look at the middle of the page) –  mg. Sep 4 '12 at 12:48
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