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Unread 07-17-2013, 05:32 PM   #5
Terry Kennedy
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Join Date: Apr 2005
Location: NYC area
Posts: 51
Default Re: A post for postings sake

Originally Posted by Trod View Post
This is actually a well known issue. Intel CPU do not support 4GB of memory on a 32-bit OS. You'll see this issue in Windows and most Linux implementations.

It IS possible to hack a patch to address it - but it can cause some instability.

AMD CPU do not suffer from this issue. If you have a Snap Server 500/600 series (All using AMD Opteron CPU) they can allocate all 4GB of memory.
The AMD Opteron was the first 64-bit x86-family CPU. As opposed to other 64-bit CPUs which preceded it, including Itanium which had such a laughably slow x86 hardware mode that a "hail mary" software emulator outperformed it by around 10-to-1.

Older (32-bit) Intel CPUs can address more than 4 GB of memory (which can also involve moving some or all of the unavailable RAM between 3.5GB and 4GB above the 4GB line, if the chipset supports it). There are driver issues when trying to access memory above 4GB in PAE mode - many non-PAE-aware drivers will simply transfer from / to the wrong address in memory.

There aren't that many x86 systems that come with huge amounts of memory but not 64-bit CPUs. As a result, PAE (even if supported by all needed drivers) is generally not a "win". For example, the Tyan S2721-533 motherboard with 4GB of RAM installed (Socket 604 Xeon CPUs) will give you a whopping 128MB "above the line" in PAE mode.

Last edited by Terry Kennedy; 07-23-2013 at 12:40 AM. Reason: Updated to clarify I menat first 64-bit x86-family CPU.
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