Windows XP Pro 32-bit with 4 GB of RAM unable to use more than 3 GB

15 pts.
BIOS settings
Memory management
Microsoft Windows XP
Windows XP Professional
Hello all, I've just installed additional 2 GB of RAM to get 4 GB in total. however OS is unable to allocate whole 4 GB, but showing addressable only 3 GB (in system properties). System BIOS and also msinfo32.exe points to 4 GB of physical memory. Any clue how to configure OS to be able to address whole amount of available memory? Or the only way to get full advantage of 4 GB of RAM is 64-bit system? more details: RAM is not shared to other HW (e.g. video adapter) I've tried to make changes to boot.ini - first I've tried /3GB switch, but it haven't helped at all, even system was not working properly (problems with NW connectivity) and was unbelievable slow. - then I've tried /PAE switch, but nothing happened. only very few information about this switch is available from MS. As far as I know part of memory (from the top) is firstly being reserved for system resources and devices (such as shared video adapter) and the rest is addressable to system and programs (addressing from the bottom). based on this I would like to find why 1 GB is reserved and to which resources, but I do not have any clue where to find it (no info in BIOS). If the reserved space is around 128 - 256 MB I would say fine, this could be for buses, controllers, etc. but 1 GB seems pretty much for me. Also when I was running with only 2 GB of RAM, almost 2 GB were shown as addressable in system properties. currently my memory usage stats looks like:
H:>pstat |more
Pstat version 0.3:  memory: 3140804 kb  uptime:  0  0:30:31.473

PageFile: ??C:pagefile.sys
        Current Size: 2095104 kb  Total Used:  73960 kb   Peak Used  76408 kb

Memory:3140804K Avail:2009096K  TotalWs:1244976K InRam Kernel: 2576K P:68780K
Commit:1127308K/ 885608K Limit:5070032K Peak:1160572K  Pool N:139140K P:69256K
See that only 3 GB are reported as total memory. Any solution is gladly welcomed. thanks in advance. PS the question is not if I need 4 GB of RAM (and what for), but if it is possible to make good use for it if needed.

Answer Wiki

Thanks. We'll let you know when a new response is added.

Here is an excellent article explaining why this is happening and that basically there is nothing you can do about it.

Please check this out.

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  • carlosdl
    By using the /3GB switch you reduced the amount of memory for the OS, and that's why it became very slow. As mentioned in the excellent article suggested by Technochic, your hardware needs to provide support to PAE in order to be able to use it.
    85,430 pointsBadges:
  • Pista
    Thanks for your replies.
    15 pointsBadges:

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