BIOS Says 4gb RAM, Vista says 3gb

[DTM426]

I recently just purchased 2x 1gb sticks of RAM from newegg, to add on to my original 2gb. This was supposed to give me 4gb of RAM. When I rebooted my computer, I checked my BIOS to see if everything was functioning correctly, and it did say that my computer has 4gb of RAM. However, when I start up Vista, I go to Start > Control Panel > System, and the system information reads that I have 3070mb of RAM in my computer. Is there a reason for this, and can it be fixed?

 

[Route44]

Is your Vista the 32 bit OS? If so it will not recognize nor utilize 4 gigs. Now if your Vista is 64 and it doesn't recognize it then that is an issue.

 

[DTM426]

Darn. Yeah, it's the 32bit OS. I didn't know it didn't utilize more than 3gb. Hm... looks like I'll have to sell one of my 1gb sticks to a buddy then! Haha, thanks for the info, very helpful.

 

[Cybersciver]

Guess you were joking about selling one of your sticks, but in case you weren't there are 2 good reasons why you shouldn't.
First is you will eliminate dual channel access mode so your memory will run slower.
Second is that Windows maps the memory of any devices with memory of their own to RAM. Also it automatically sets aside about 250MB for other devices. So, if you've got a GTX with 768MB of GDDR3 you only have about 3gigs of available memory anyway, and Windows 32 can access all of it.

 

[SNGX1275]

If it will make you feel better to see Windows report 4GB, then just wait it out until SP1 is released. They are going to 'fix' this issue which doesn't change anything in how Windows utilizes it, but it will display 4GB.

 

[DTM426]

Yeah, I figured I'd keep it in for dual channel purposes, but I didn't know the rest. Thanks.

 

[subcan]

There is a Microsoft Techinical Bulletin regarding this issue. Your video card will use up some of this 4GB of ram and that is why it reports up to 3.12GB of Ram available. Here is the link: you will have to copy it to the address bar. I am not powerful enough yet to post with links or images <hehe>
support.microsoft.com/kb/929605/en-us

 

[hanaleia]

Vista WILL recognise 4GB of RAM

I just had the same issue on my Acer Aspire 5050 laptop, after installing 4GB of RAM yesterday only 2 showed up, After Installing SP1 for Vista, I found out that
SP1 has addressed the issue and after installing it 'Viola' I now have all 4 Gigs of Ram showing on my 32-bit Vista laptop. I may actually keep Vista on my laptop now, it also fixed several other issues I had been having, so before you go fiddling with a bios flash you may want to give it a try.
"SP1 for Vista, good for what ails you"

 

[SNGX1275]

Yeh, SP1 'fixes' how it displays. But its just a cosmetic thing to hopefully quiet the masses of people that don't understand why it was showing less than that originally. This 'fix' doesn't change anything in how the OS behaves and utilizes the RAM though.

 

[chirag_gada]

hey that was a bug in vista.... its been taken care of in service pack 1...

 

[SNGX1275]

Its not a bug. In effect Microsoft created an error just to keep people that don't know how memory is reserved in a 32bit OS from constantly complaining about 'incorrect' RAM reporting.

Raymond Chen has this to say

In the absence of the /PAE switch, the Windows memory manager is limited to a 4 GB physical address space. Most of that address space is filled with RAM, but not all of it. Memory-mapped devices (such as your video card) will use some of that physical address space, as will the BIOS ROMs. After all the non-memory devices have had their say, there will be less than 4GB of address space available for RAM below the 4GB physical address boundary.

Ian Griffiths gives some more detail:

To address 4GB of memory you need 32 bits of address bus. (Assuming individual bytes are addressable.) This gives us a problem - the same problem that IBM faced when designing the original PC. You tend to want to have more than just memory in a computer - you need things like graphics cards and hard disks to be accessible to the computer in order for it to be able to use them. So just as the original PC had to carve up the 8086's 1MB addressing range into memory (640K) and 'other' (384K), the same problem exists today if you want to fit memory and devices into a 32-bit address range: not all of the available 4GB of address space can be given over to memory.

For a long time this wasn't a problem, because there was a whole 4GB of address space, so devices typically lurk up in the top 1GB of physical address space, leaving the bottom 3GB for memory. And 3GB should be enough for anyone, right?

So what actually happens if you go out and buy 4GB of memory for your PC? Well, it's just like the DOS days - there's a hole in your memory map for the IO. (Now it's only 25% of the total address space, but it's still a big hole.) So the bottom 3GB of your memory will be available, but there's an issue with that last 1GB.

Here is an illustration about it: (Stolen from CodingHorror but not hotlinked)

So all Vista SP1 did, was cosmetically 'fix' this so the true amount of RAM avaiable to the OS is no longer showing, and instead shows the total amount of RAM installed. They didn't fix a bug, they changed what they are reporting.

More detailed on the material in this post can be found here, where most of what I said was taken from.