Slot or Memory - Can't tell

[ggtsu]

Been working on my buddy's new comp, but I can't get this machine to recognize all 4 gigs of ram. It's using a DFI lanparty nf4 sli-dr mobo and 4 sticks of 1gb G-skill 3200 DDR 400. When all 4 are installed, it seems to run fine, but only 3gb are recognized. If I only use one at a time, everything seems fine as well. Now, as I add them in, one at a time, everything works until I get to the third stick (going from slot 1->3->2->4). When it powers up, I only get an error beep. Now if I go ahead and fill the 4th slot, it boots up. However, it still won't recognize all 4 gigs. Am I dealing with bad memory, bad motherboard, power? Is there anything I can use to see which slot isn't being recognized? Ran memtest, it only saw 3 gigs as well.

 

[Mex]

Your RAM is fine. The problem is Windows. Under 32-bit, the total amount of memory that the OS can recognize is 4GB. The operating system has to allocate a certain amount of memory to certain fuctions of the computer such as for PCI devices, etc. With 4GB, this allocated amount can reach as high as 1.5GB.

The only solution is to use 64-bit, although there is also the "Physical Adress Extension," which I can't explain.
http://www.microsoft.com/whdc/system/platform/server/pae/default.mspx

 

[ggtsu]

I forgot to mention, with all 4 gigs installed, the bios only shows 3 gigs.

 

[Mex]

This website claims that the system BIOS is one of the "functions" that memory is allocated to.

- System BIOS (including motherboard, add-on cards, etc..)
- Motherboards resources
- Memory mapped I/O
- configuration for AGP/PCI-Ex/PCI
- Other memory allocations for PCI devices

The limit for my board is 512MB, so I don't have any experience with this problem. To be honest, unless your friend is doing some kind of memory-intensive task (Think CAD or something like that), he doesn't need 4GB.