Only 3.37GB of RAM on x64 when BIOS says 4GB

Can anyone help me understand why Windows reports "4.00 GB (3.37 GB usable)" under Installed Memory?

OS: Windows 7 Ultimate Build 7100 x64
Installed RAM: 4 GB (2 x 2GB)

When I installed Win7 originally (I started with the initial beta build), it reported 4.00 GB without specifying a lower 'usable' amount... I never bothered checking again and just happened to notice the change last night.

I've tried checking the interwebs for answers but everything I can find refers to having 32-bit... blah, blah. I understand all that, but I have 64-bit so I'm under the impression that I should be able to use all of it. I also don't think this is a limit on my motherboard... it specifies it's able to handle up to 8 GB.

Any help would be great. Thanks.

Vvildcard

Can you please paste back the results of running this from a CMD prompt:

systeminfo |find "Memory"

Do you have a video chip onboard your motherboard that takes up 512MB for itself? You can disable it if you have a video card.

Systeminfo |find "Memory"
Total Physical Memory: 3,455 MB
Available Physical Memory: 2,452 MB
Virtual Memory: Max Size: 6,908 MB
Virtual Memory: Available: 5,149 MB
Virtual Memory: In Use: 1,759 MB

No onboard video. I have a GeForce 8800 GTS that shouldn't be getting any of the system RAM. That said, I'm not 100% sure how to check that.

Check your BIOS for a option called memory mapping, or something to that effect, and enable it.

Check MSCONFIG.
Boot
Advanced Options
Maximum Memory

Make sure there is no check mark.

.

Okay, I think I have it all figured out... Apparently my motherboard and/or BIOS is a pile of [badword] and doesn't actually have the 64-bit compatibility I thought it had. I built it a long time ago and was looking at the wrong online manual. Basically, after some research, I've discovered Intel's 945 chipset "appropriates" a certain amount of RAM to itself. In my case, this is 640 MB, leaving me with the 3.37 GB for the OS.

I'm going to check for a BIOS update, but I'm not crossing my fingers. Worst case scenario, I'm happy knowing why this is happening.

Thank you all for your help... I'm very happy to have found this forum.

Vvildcard

Not that I'm encouraging you to spend more money, but you could get a good 965 board very cheap these days. I know this, because I have a few to sell, and have been disappointed in what their value is.

Yep - I have the same 'problem'. I have a Lakeport 945P chipset in my Dell:

List of Intel chipsets - Wikipedia, the free encyclopedia

And as the Note on the Wikipedia page states:

'Lakeport chipsets lacks support for remapping memory; the size of addressable memory space may be less than 4 GB, regardless whether the processor operates in 64-bit mode.'

For me, Windows actually reports 4GB installed physical memory, but then goes on to state 'Total Physical Memory = 3.581GB'.

Not that it affects me. The 945 chipset is the same reason I can't run anything more than a Pentium D. I have maxed out this PC, but the performance is more than enough to give a very good experience with Win 7, particularly now I have fitted my SSD

ceejay said:

For me, Windows actually reports 4GB installed physical memory, but then goes on to state 'Total Physical Memory = 3.581GB'.

It was Vista SP1 that introduced the practice of reporting an "installed" value which could be different to the amount actually accessible by the OS. I think the white lie is primarily meant to assuage consumer concerns over a highly technical problem that's difficult to explain to most people - "I paid the store for 4.0GB, how come Windows says there's only 3.x in my machine?!?"