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32-bit Windows and the dreaded (and misunderstood) 4GB RAM limit
Darwin:
I would expect you to have 4Gb - 512Gb of video RAM = 3.5Gb visible to Windows - so the question is where has the other half a gig gone?-Carol Haynes (September 08, 2008, 04:10 PM)
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My thinking exactly!
What other devices have you got that might use mapped memory? Check you device manager and check for memory mapped devices and see what has gobbled up you new memory!
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Right - I'll check this out... AFAIK, there shouldn't be anything else using mapped memory. However, I am *guessing* that my ethernet cards, sound card (which is integrated), keyboard, touchpad, built-in webcam, may be contributing to this. I'll take a look when I get a chance (I'm on my XP machine at the moment).
From what I read (and its been a while so I may be wrong) enabling PAE in 32-bit XP doesn't actually do anything at all.
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This is more or less my take on it as well. Once again - I've seen a lot of conflicting reports. The people I trust say it's a waste of time though (can't remember who those people are, off-hand).
Thanks for taking the time to answer, Carol, and everyone else.
tomos:
another question:
if this memory is not available to the 32-bit OS - does that mean it's also unavailable to programmes on the computer ?
Carol Haynes:
Yes - it is simply mapped to devices in the memory map and the actual physical memory is unused.
Paul Keith:
I'm a newb at this thing. What platform can support 4gb? I thought Vista was 64-bit?
Carol Haynes:
XP and Vista both come in 32-bit and 64-bit 'flavours'. As I understand it there are restrictions in 64-bit XP to maintain software compatability - though you may be able to enable PAE to extend the addressable memory. I haven't tried Vista 64 but I think it supports up to 8Gb.
The big problem is application compatibility. If software is written and compiled to run on 32 bit windows none of the memory addresses have enough bits to address more than 4Gb of physical memory because they are all 32 bit addresses. If software is compiled for 64 bit windows then it has 64 bit addresses and can address a huge amount of RAM - though MS have restricted the physical amount of RAM that can be actually used artificially. Some server products are less restrictive.
That's a simplistic view (I am simple) and may or may not be wholly accurate but it gives the idea.
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