[chadfree] Troubleshooting a Memory Problem During a System Upgrade
- From: "Mike" <mikebike@xxxxxxxxx>
- To: Computer_Help_and_Discussion@xxxxxxxxxxxxxxx, chadfree@xxxxxxxxxxxxx
- Date: Thu, 13 Oct 2005 13:56:53 -0700
Troubleshooting a Memory Problem During a System Upgrade
http://list.windowsitpro.com/t?ctl=166A9:94C6A
From; Windows IT Pro http://www.windowsitpro.com/
Commentary: Understanding Available Memory ====
by David Chernicoff, david@xxxxxxxxxxxxxxxx
My recent column about memory concerns with a desktop system upgrade
(see the URL below) generated a lot of reader response, most in the
"please follow up on this issue" vein. But a surprising number of
readers asked questions that made it clear they don't understand how a
computer and OS utilize memory.
From the OS's perspective, the amount of memory available to the OS is
the amount that the hardware reports is available, regardless of how
much memory is physically installed an enumerated. That was the issue
that generated my original concern: a 4GB system that reported only
3200MB of available memory to the OS.
I found the answer to my original question in the support documentation
for the motherboard: "On a system with 4GB of system memory installed,
it is not possible to use all of the installed memory due to system
address space being allocated for other system critical functions." I
knew that system resources took memory space but was surprised by the
750MB being reserved for PCI Express features. A few readers told me
that their server-class systems had motherboard settings that let them
move the PCI memory space above the 4GB line; that feature isn't
available in the family of desktop motherboards I'm using.
Readers also pointed out that if I use 64-bit Windows, I can map the
system resource memory to another location so that the physical memory
will be available for applications. I plan to install 64-bit Windows as
an alternate OS on this computer, but none of the applications I use on
a daily basis are available yet in native 64-bit versions.
But what I want to address this week is a clear misunderstanding about
how system memory works. I received several email messages that asked
question such as, "Does this mean that I can't use PCI Express on a
system that has only 512MB of RAM?" or "Will I only have 256MB of
useable memory in a 1GB system?"
Neither of those situations is a problem. The system resources aren't
taking away large chunks of installed memory; the system resources
reserve memory space at the top of the 4GB memory range addressable by
a 32-bit processor. If this system board has less than 4GB of physical
memory installed, the memory use is pretty much invisible to the user.
Only when a user has 4GB of physical memory installed does the problem
become obvious.
The computer that I used to generate this column reports 896MB of
memory reserved for system resources (down from 1126MB after a BIOS
update) and 3200MB of memory available to the OS. This means I paid for
a fourth 1GB bank of RAM that's effectively unusable; the system would
have the same performance and virtually the same OS memory if I had
installed only three banks of 1GB memory. This problem doesn't affect
systems with 3GB of memory or less. It will be a concern only to those
of us who find a need for the maximum amount of memory the system
claims to support. The reality of the situation is that with a 32-bit
OS, motherboards that support PCI Express and can't map memory above
4GB, won't have the full 4GB addressable range of memory available to
applications.
Troubleshooting a Memory Problem During a System Upgrade
http://list.windowsitpro.com/t?ctl=166A9:94C6A
Mike ~ one of the Moderators
It is a good day if I learned something new.
Editor MikesWhatsNews http://www.mwn.ca/
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