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Weird question: In the office whe are discussing if whe have a machine that is 64bit infrastructure (hardware) with a 32bit OS (Server 2008 std) and 8 gigs of ram.

The OS detects the full 8 gigs of ram, BUT, being a 32 bit OS, will the OS use the full 8 gigs of ram?

How can we prove how much ram is really being used, or Windows Server is fooling everybody?

more: whe need some tests done, is there any benchmatking software out there for this purpose?

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Why the downvotes? – Axel Gneiting Mar 23 '11 at 23:39
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^^ This. This is quite an interesting question with some useful stuff coming out of it. – Linker3000 Mar 23 '11 at 23:46
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up vote 8 down vote

A 32-bit OS using PAE can access up to 64GB of physical memory, but a process running on it will still be restricted to 4GB unless it uses a hack such as AWE.

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Even with PAE, the 32-bit kernel has hard-coded memory limits for a few purposes. So you may have unused memory and still be memory starved. – Zoredache Mar 23 '11 at 23:32
plus using PAE is usually slightly slower – mbx Mar 23 '11 at 23:33
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This is not entirely correct. One process can only use 2 GiB of virtual address space when running on 32 bit Windows, because the rest is used by the kernel (3 GiB if the /3G kernel parameter is used and the executable has the "large address aware" flag set). – Axel Gneiting Mar 23 '11 at 23:36
@mbx: Context switches are certainly more costly, but is this really measurable? – Axel Gneiting Mar 23 '11 at 23:38
@Axel: Sure, but it can still access 4GB, even if it can't write to all of it. – Ignacio Vazquez-Abrams Mar 23 '11 at 23:56
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up vote 1 down vote

SQL Server definitely uses it with AWE enabled so there's your not-just-theoretical proof. Even without AWE, any one process could only access 2 GB but if you have multiple such processes you can use it all.

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up vote 0 down vote

You could try to verify it by disabling swap space and creating some 2g consuming processes. Consuming as in random data (to prevent Copy-On-Write and lazy access to unused pages).

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