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Comment by thechut | Hacker News Reader

I dual boot Ubuntu 12.04 32-bit and Windows 7 32-bit on my HP laptop, it has 8GB of RAM. When I am running Ubuntu I see 7.8GB (I'm assuming this is 1000 vs 1024 issue and doesn't concern me) in my system settings and resource monitor. When I am running Windows I only see 3.8GB of RAM in resource monitor, but I see the full 8GB if I look in device manager. Can somebody explain this to me?

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It is a licensing restriction. Windows Server supports up to 64 GB on 32-bit versions: http://msdn.microsoft.com/en-us/library/windows/desktop/aa36...

>> I'm assuming this is 1000 vs 1024 issue

It'll likely be your graphics card uses a portion of your main RAM for its memory. This is common.

I'm not sure this is true for discrete cards. Onboard GPUs will utilize good chunks of system memory (and this is configurable in the system BIOS generally), but discrete cards don't use any afaik.

It has been said here before. Linux fully supports PAE whereas Windows only uses it for execution restriction. Therefore you are not able to see anything beyond the 4 GB limit on Windows.

Sorry, didn't see it. Thanks for your response, that makes sense!

> Linux fully supports PAE whereas Windows only uses it for execution restriction.

That is not correct. Windows also supports full PAE, but adds licensing-based restrictions. The Datacenter and Enterprise editions of Windows Server 2008 will provide access to all 64GB RAM PAE can provide.

You might be interested to know that Windows keys don't discriminate between 32-bit/64-bit. If you can find installation media for the same type of x64 distribution (Home, Pro, etc) as your 32-bit, you can install x64 and use your current key. May be worth the reinstall to get access to your RAM.

Of course, you might make sure that appropriate drivers for your laptop exist for x64. I would hope any laptop that can accommodate 8GB would have x64 drivers.

Most likely your Ubuntu uses PAE, and Windows does not. NT kernel certainly supports PAE, but likely MS has disabled it in client systems for some reason.

> NT kernel certainly supports PAE, but likely MS has disabled

Nope. They can't actually disable it since the NX bit requires that PAE be enabled.

The limitation comes from licensing and tiering, and is handled in the kernel independently from PAE.

I'm not an expert on these matters, but as I understand it, Windows is not ignorant of the fact that you have 8GB of RAM, it is simply unable to address it. So it makes logical sense that it would show you having 8GB, but only 3.8GB of usable RAM.

That is not correct, Windows is actually fully aware of the physical RAM on the machine and is technically able to use it, but has a license-based restriction scheme only letting a subset of the RAM be used.

> I'm assuming this is 1000 vs 1024 issue I think rather some of the address space has I/O ports mapped to it, both in Windows and Linux.

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