ANSWER: Why doesn't my system detect all 4GB of RAM?

[Zap]

Because you need a 64-bit operating system, that's why!

There are more technical reasons regarding memory addressing space and such, but that's the gist of it. Typically a Windows XP system will see around 3GB RAM, give or take.

 

[taltamir]

Excellent thread. We need to spread the good word.
If you have a 64bit OS and some RAM is missing, its because you have integrated graphics and its using up some of your system ram (it doesn't have its own)

 

[Absolution75]

Thank you so much - I was getting bored of reading the same thread every few days

 

[alaricljs]

If you have a 64bit OS, 64bit CPU, 4+GB of RAM, and are still seeing 3.xxGB of RAM that means you're probably on a "transition period" laptop where the chipset between the CPU and RAM is 32bit. A Dell D820 is a perfect example of this.

 

[hanspeter]

Another why is that memory remapping must be enabled

 

[taltamir]

Another why is that memory remapping must be enabled

oh yes, that too... i was trying to figure out why my dad's computer was missing some of his 2GB of ram despite having Win7 64bit... so i thought memory remap was not working. I saw that there was no bios option so i asked the manufacturer if its hidden somewhere or renamed... they told me "IGP". and I went *facepalm* "DOH!"

 

[Nothinman]

And this only applies to 32-bit Windows desktop OSes.

Other 32-bit OSes like Windows Server Enterprise, Linux, FreeBSD, etc can properly use PAE to address up to 64G of physical memory. And, at least on Linux, you can install a 64-bit kernel on a 32-bit install in order to get access to all of your memory and still maintain maximum compatibility by running a 32-bit userland.

 

[pjkenned]

The other issue is that people with shared memory GPU architectures will not see 4GB even in 64-bit OSes if the memory is partitioned at the north bridge level. If this is going to be a sticky, we should probably make the answer correct.

 

[hal2kilo]

If you have a 64bit OS, 64bit CPU, 4+GB of RAM, and are still seeing 3.xxGB of RAM that means you're probably on a "transition period" laptop where the chipset between the CPU and RAM is 32bit. A Dell D820 is a perfect example of this.

Dell Inspiron 1505E also.

 

[dualsmp]

Some motherboards reserve memory in hardware. My MSI H55 mobo exhibits this behavior even with a discreet video card in place, which should disable the Intel HD integrated graphics. On my MSI it reserves 137MB of memory and shows 3.87GB usable in Win7 x64. I think this can happen in both the H55/H57 series.

In my case though the latest BIOS update might have finally fixed this problem but have yet to try it.