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View Full Version : OT Question about Windows XP and 4GB of Ram. Does it support it? Here's why!



Mysticpuma2003
04-30-2007, 09:26 AM
Ok, this page from Microsoft confuesed me. I was sure that XP Pro and MCE only support 3Gb of Ram because of this thread:

http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx

however halfway down the page it says:

"Windows XP Professional and Windows Server 2003 Memory Support. The maximum amount of memory that can be supported on Windows XP Professional and Windows Server 2003 is also 4 GB"

So Microsoft say that it does support 4Gb.

This is great news if it does, but I can't make head-nor-tail of the Microsoft speak on the above link.

So can it or can't it?

Thanks, MP.

Mysticpuma2003
04-30-2007, 09:26 AM
Ok, this page from Microsoft confuesed me. I was sure that XP Pro and MCE only support 3Gb of Ram because of this thread:

http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx

however halfway down the page it says:

"Windows XP Professional and Windows Server 2003 Memory Support. The maximum amount of memory that can be supported on Windows XP Professional and Windows Server 2003 is also 4 GB"

So Microsoft say that it does support 4Gb.

This is great news if it does, but I can't make head-nor-tail of the Microsoft speak on the above link.

So can it or can't it?

Thanks, MP.

striker-85
04-30-2007, 09:37 AM
XP Pro will support 4GB of RAM but only 3GB of RAM is available for use by applications. The other 1GB is reserved for use by the OS itself.

Normally the split would be 2GB applications and 2GB OS, but the /3GB switch allows apps to use 3GB.

Agamemnon22
04-30-2007, 09:39 AM
In theory it supports 4gigs and more via PAE (http://www.microsoft.com/whdc/system/platform/server/PAE/pae_os.mspx)

However, any one program is still limited to a 2gig chunk. So you might have 4 gigs, but not be able to run a program that requires 3. At the same time, you could run 2 instances of a program that requires 2. Ya see?

striker-85
04-30-2007, 09:45 AM
PAE is an Intel-provided memory address extension that enables support of greater than 4 GB of physical memory for most 32-bit (IA-32) Intel Pentium Pro and later platforms.

http://www.microsoft.com/whdc/system/platform/server/PAE/PAEdrv.mspx

PAE is not needed for 4GB which is the max XP Pro can support.

Applications can use the 3GB of memory. No APIs are required to support application memory tuning. However, it would be ineffective to automatically provide every application with a 3-GB address space.

Executables that can use the 3-GB address space are required to have the bit IMAGE_FILE_LARGE_ADDRESS_AWARE set in their image header. If you are the developer of the executable, you can specify a linker flag (/LARGEADDRESSAWARE).

http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx

No601_prangster
04-30-2007, 09:57 AM
Also be aware that the 4GB limit includes your video memory as my friend with 4GB of memory and two 750MB 8800 cards in SLI found. He could only access two and a half Gigs of his system memory! He's now going to move to 64 bit.

crazyivan1970
04-30-2007, 10:29 AM
3GB switch is really server option... i doubt you can set it on XP Home or even Pro. Normally OS restricts 1 process to exceed 2GB, that`s why 3GB switch is being set. Applications can take up all the memory, but cannot exceed 2GB each... or 3GB is switch is set. If i remember correctly Win2003 server has that feature, Win2k server does not.

striker-85
04-30-2007, 10:32 AM
/3GB switch can be set on XP Pro but not XP Home.

Read the link for info:

http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx

jarink
04-30-2007, 11:47 AM
Confusing things even more is that the /3GB switch only affects the virtual address space available to applications. It really doesn't have much to do with physical RAM.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">From MS:
Operating systems based on Microsoft Windows NT technologies have always provided applications with a flat 32-bit virtual address space that describes 4 gigabytes (GB) of virtual memory. </div></BLOCKQUOTE>

Virtual address space is a memory mapping mechanism that uses physical RAM or a swap file as needed.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">From MSDN:
The maximum amount of physical memory supported by Microsoft Windows ranges from 2 GB to 1 TB, depending on the version of Windows. For more information, see Memory Limits for Windows Releases. The virtual address space of each process can be smaller or larger than the total physical memory available on the computer. The subset of the virtual address space of a process that resides in physical memory is known as the working set. If the threads of a process attempt to use more physical memory than is currently available, the system pages some the memory contents to disk. The total amount of virtual address space available to a process is limited by physical memory and the free space on disk available for the paging file. </div></BLOCKQUOTE>

As striker-85 said, the reason XP is limited to 4GB physical RAM is that MS does not include PAE support in it. PAE is what's essential to supporting more than 4GB memory addressing in a 32-bit operating system. 64-bit OSes already have the ability to map more memory (because they have twice as many 'bits').

No601_prangster, this may answer your friend's issue:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">From MSDN: (http://msdn2.microsoft.com/en-us/library/ms791558.aspx)
On Windows XP, some drivers, especially video adapter drivers with onboard RAM, cannot run with the /3GB parameter because they require more address space than the 1 GB kernel address space permits. </div></BLOCKQUOTE>

willyvic
04-30-2007, 12:40 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by No601_prangster:
Also be aware that the 4GB limit includes your video memory as my friend with 4GB of memory and two 750MB 8800 cards in SLI found. He could only access two and a half Gigs of his system memory! He's now going to move to 64 bit. </div></BLOCKQUOTE>

This is the second time I've seen something like this posted. In all the links I do not see where Video Memory is subtracted from OS memory.
Can you please elaborate, perhaps with sources?

Curiously waiting,
WV

striker-85
05-01-2007, 10:06 AM
Hi WV,

I posted a reply to this at:

http://forums.ubi.com/eve/forums/a/tpc/f/49310655/m/1511089355

willyvic
05-01-2007, 10:18 AM
Yep, got it. Thanks.


WV