Re: 4GB Physical Memory Support

You might want to check MSinfo32 before and after to see what might shed some light on the issue.

CR-Sac wrote:
Hate to be the party pooper of the group here, but we're a bit off topic. Whether or not 4GB of physical memory is necessary is a moot point, the question remains why changing the page file size altered the amount of physical memory recognized by Windows. M.I.5¾ points out the existence of the "PCI Hole", which I already understand and expected. However, keep in mind that the PCI Hole exists as a result of addressing done by the BIOS, not by Windows. Also, since Windows is in PAE mode it can address much more than 4GB of RAM. Each application only has 4GB of virtual memory assigned (a combination of physical memory and page file space), but Windows itself is capable of managing and addressing a full 4GB of physical memory, so long as the motherboard appropriately support memory remapping to workaround the PCI Hole. The problem here still remains: the PCI Hole explains the missing .52GB of memory, but it does not explain why this hole increases when the Page File gets bigger. So my original question still remains.

"M.I.5¾" wrote:


"Michael W. Ryder" <_mwryder@xxxxxxxxxxxxxxxx> wrote in message news:RRbzi.454090$p47.424391@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

M.I.5¾ wrote:

"CR-Sac" <CR-Sac@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message news:2463F3F7-EE57-484D-BC83-3536C57DA57D@xxxxxxxxxxxxxxxx

So I understand both the PCI Memory Hole, the 4GB limitation for physical
memory within Windows itself, and the 4GB of total Virtual Memory Address
available to each process, etc. etc. However, I have run across a situation
that I find very odd.
A new build consisting of an Intel E6750 2.66GHz Core 2 Duo with a
1333MHz FSB, Intel DG33BUC motherboard, and 4GB of DDR2-6400 clocked down to
667MHz running Windows XP Professional first recognized only 3.23GB of
physical memory installed. Also, Windows had automatically loaded into PAE
mode to support DEP since it's built into the processor. My first impression
was that the missing .77GB of physical memory was a victim of the PCI hole.
But what confused me was that after tweaking the Page File size downward the
reported physical memory increased to 3.48GB. Out of curiosity I completely
removed the page file, but the reported physical memory did not change.
After returning the page file to the "System Managed Size" the reported
physical memory remained at 3.48GB. Finally, when reverting to the original
custom settings populated by XP during the initial setup of the system the
physical memory shrank back to 3.23GB.
This is clearly not an issue of the PCI Hole or 4GB limitation. So what
is the problem?

The 32 bit version of Windows XP only supports a maximum of 4 GB of memory space. However, what you have overlooked is that all the memory mapped bits of hardware also have to occupy this space. Normally with smaller amounts of memory, this isn't a problem, the memory mapped hardware occupies addresses for which no physical memory is present. Once 4GB is installed the latter part of it isn't available because something else has already pinched the address range. 3.2 to 3.4 GB is about the right ball park for the memory that is available.

The only mystery that remains is: why you think you require 4GB of memory in the first place?




Obviously you have never tried to edit large (1 GB+) files. I have 3 GB of RAM and have had it use all of it plus a large swap file when trying to open it with Wordpad or some other programs. My normal memory usage is 1.5 to 2 GB of memory with just my normal programs open.


I regularly edit files much larger than that. What makes you think large amounts of memory are required for editing large files? Never heard of a hard disk? Windows will generally occupy whatever memory you install, requiring less swap file as the memory gets bigger. 512 MB to 1 GB is generally adequate for most purposes, but editing High Definition video is often more comfortable with 2GB. I cannot think of anything that needs any more than 2GB, but there may be some very specialist applications out there that benefit from it. Otherwise there is seldom much performance gain going from 1GB to 2GB let alone up to 4GB.






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Relevant Pages

  • Re: 4GB Physical Memory Support
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