RE: Windows XP does not recognize memory upgrade
- From: KrisR <KrisR@xxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 25 Nov 2008 06:08:05 -0800
Thank you for the various suggestions. They have helped in researching this
problem further and increasing my knowledge about what's going on. It is
certainly not a problem of malfunctioning hardware.
The basic problem is that of limited address space on a 32-bit computer.
In terms of the memory mapping - 2^32 = 4GB is the number of addresses
available. The system resources (System ROM, APIC(s), Integrated PCI devices
- such as network connectors and SCSI controllers, Graphics card and more)
have priority and get their addresses assigned first (otherwise they wont be
accessible) and the rest - Less than 4GB- is left for the user RAM.
Now its not that the remainder is used for anything\eaten up and so on - it
simply not mapped, which means that these memory locations have no addresses
that can be used to refer to them for read\write operations.
My calculation is approximately as follows:
For a start Windows XP always allocates around 750MB of the high end
addresses for non-memory use. If you have a lot of extra devices installed,
XP takes more.
In particular graphics cards are greedy. As I have two cards each with 512MB
of memory, 1G goes away right there. Given that I have many devices
installed, it is quite possible that all of my addresses above 2GB have been
taken.
I cannot be entirely sure of this though. I still cannot satifactorily
explain why XP reports *exactly* the same amount of user memory (2096172KB)
irrespective of installing 2GB or 4GB of physical memory. I should wish there
was a tool that could give me a complete memory map of XP. Anyone who knows
such a tool?
I need my graphics cards, so I shall just have to live with the limitation
of 2GB. That is not bad either :-) I also decided to keep all of my new
memory memory kit, even if only half is used, because this is faster memory
than I had before. I could have installed only one stick of 2GB, but the
benefit of dual channel is significant. As measured by PC Wizard, dual
channel gives 40% better memory performance and 6% global overall performance.
Again, thanks for the help!
"KrisR" wrote:
I have upgraded my memory from 2GB to 4GB, using a set of matched 2x2GB.
memory sticks.
During boot the BIOS correctly reports that installed memory is 4096 MB.
However, XP does not seem to recognize the memory upgrade.
The System Properties panel still reports "2.00 GB of RAM"
and the Task Manager says:
Physical Memory (K) 2096172
I realized that XP cannot get all of the 4GB, but I had expected to get at
least 3GB.
I have tried to set the /3GB boot parameter, but to no effect.
What is the problem?
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