Why would windows only recognise half a stick or RAM?

Question

I was at the in-laws over the weekend and one of the machines was reported as having got much slower recently. After some investigation it seemed that windows was reporting only 384mb of ram, and this was most likely the culprit for the slowness. I opened up the machine to see what ram it took and it had 2 slots, both with 256mb sticks in them.

Why would only 1/2 of one stick be being recognised?

I should have looked in the bios to see what it claimed to have, but didn't and I'm not there now so I can't.

Any ideas?

EDIT: The machine is a Packard Bell IMedia. Not sure which model. The mother board is an asus p4r800-vm, but seems like a custom model as only 2 ram slots not 4. Windows is XP SP3. No access to the machine now, but was just curious as to any ideas why this might be. No idea if this is a new development or not as not really seen the machine before. The graphics allocation seems like its probably right.

Answer 1

I'd guess that some of the ram has been allocated for use by the graphics card. It's usually a setting in the BIOS

Answer 2

I suppose you are having 2x 256MB RAM installed which sums up to 512MB. If you are using onboard video instead of a dedicated graphics card, chances are that your BIOS is set to use 128 MB as shared memory for your onboard video.

You should lower the shared memory usage in the BIOS to 32MB or less or install a dedicated graphics card. The last option probably restores most of the performance.

If there's a memory detection problem as others suggest and you are using two identical memory modules, it would only recognize 256MB of memory.

As the current memory situation was probably the same before the slowdown, I'd suggest you better scan for trojans and rootkits with specialized scanner software like Spybot Search & Destroy, Hijack This or PCTools Spyware Doctor (freely available thru google pack). Often sudden slowdowns are causes of such infections.

Answer 3

Has the full amount of RAM been recognised in the past and only now stopped being seen?

If it has not recognised it all for all time, then it could be a strange chipset limitation on the motherboard - does the full amount of RAM appear during the power-on-self-test phase? Is it listed in the BIOS setup screen? If not, check to see that you have the latest BIOS for that model.

It might help to provide a little more detail in your question:

• the mothboard made+model and chipset (these are probably presented in the BIOS setup screens)
• the Windows version and service pack level (in most Windows variants the winver command will tell you this)

Answer 4

Some motherboards have troubles recognizing double-sided RAM chips. However, for this to be the case, motherboard would not recognize it from first insertion onward. If same chips once reported full capacity, I would assume some hardware/firmware malfunction.

Graphic card address space is allocated way above 512 MB so I would count that out.

Answer 5

It's a weird situation to recognize 1/2 of 1 stick of RAM - usually it's all or nothing. Check if there might be some RAM disk utility running in the background and a RAM drive is created?

Answer 6

I've seen this once, and in that particular case the memory was clock at a higher speed than the motherboard would deal with. But other than that I have no idea why that might be the case.

Answer 7

I have had machine in the past that have limitations on the amount of addressable memory. An old HP had exactly the same problem - regardless of what amount of memory I put in, it would never see more than 384MB.

I would guess that it's a limitation of the motherboard, and don't think it's a windows limitation - check the BIOS to see how much it's actually recognizing.

Answer 8

I'm having the exact same problem with the exact same motherboard. No matter what piece of 512MB I insert, it only sees 384MB. :S