Old motherboard only recognizes half the memory - even if only one chip is in

I have an old Asus P2B-S motherboard and went to the Crucial systemscanner to find the right memory for it, then bought it on a cheaper site.
Now my BIOS only recognizes half the RAM. If I put one 256MB chip in, it shows 128MB.
The max for this motherboard is 1GB, and that's how much I bought, but I can't use it...
The old RAM I have in there is less than 512MB altogether and works normally.
The memory I bought (4 sticks) was:
Kingston KVR133X64C3/256
256MB PC133 DIMM CL3
The motherboard specs say PC100, but that seems to be downward compatible.
Any idea why it doesn't work?
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Gary CaseConnect With a Mentor RetiredCommented:
leew -- BX chipsets do NOT "require" ECC RAM.   They DO, however, require dual rank DIMMs (regardless of whether they're ECC or not) to use 256mb modules.   This system will work fine with non-ECC memory modules;  but they do have to be dual rank.

semmelbroesel -- as leew noted, you could not have got a Kingston part # on the Crucial scanner.   You might find the same Crucial module for less elsewhere (sometimes you can);  but if you wanted to be sure you had the right Kingston module you should have used Kingston's memory selector.
You apparently bought single rank DIMMS -- so the system is only "seeing" 1/2 of the memory.

Lee W, MVPTechnology and Business Process AdvisorCommented:
You couldn't have bought the same memory as you found on crucial - crucial doesn't sell Kingston memory.  They are two different companies.

That board uses a BX chipset which required ECC RAM if you were using 256 MB DIMMs.  Standard non-parity RAM cannot see sticks properly above 128 MB each.  The RAM you bought is NON-PARITY (NON-ECC).
Lee W, MVPTechnology and Business Process AdvisorCommented:
If you are going to use a tool to look up RAM, either buy from the vendor whose tool you use OR at least buy the same product number and you can avoid these problems.
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Lee W, MVPTechnology and Business Process AdvisorCommented:
Wrong term - REGISTERED SDRAM (Is that supposed to be the same as Dual Rank?  I have several 440BX based boards and the only memory I've seen compatible (over 128 MB modules) is ECC Registered RAM.  Here's the manual for several of my boards:

Per PDF page 11:
512 MB unbuffered SDRAM or maximum of 1 GB registered SDRAM memory in 4 168-pin DIMM sockets.
Gary CaseConnect With a Mentor RetiredCommented:
I have a 440BX board right here with 1GB of RAM (an old Dell) -- using non-ECC memory.

The SuperMicro motherboards detailed in the manual you referenced have memory controllers designed to mix EDO, unbuffered SDRAM, and buffered SDRAM ("registered").   An interesting combo !!   I'm sure the different capacities are due to the bus loading of the unbuffered modules.   The capacity of the various motherboards depends on the design of the motherboard, and on the loading it can support (how many banks).

Registered is NOT the same as dual rank.   Registered means the module has a buffer to hold the address and control signals -- so the loading on the memory lines is much lower with registered modules than unbuffered modules.   Result:  better stability -- that's why it's usually used in servers.   Both unbuffered and buffered ("registered") memory is available in both single rank and dual rank modules.

semmelbroesel --> Now that I think about it, I'm not sure if the system I have required dual rank or single rank (it's not open at the moment -- and I don't have time to look now as I've got to finish packing for a trip => need to catch a few hours shuteye as we've got a 6AM flight).   I may have misspoke about whether the system needs single or dual rank -- but in either event it needs the OPPOSITE of whatever you bought !!  (in general single rank = chips on one side only;  dual rank = chips on both sides)

semmelbroeselAuthor Commented:
Geeze, there's so much more to memory than I thought. I thought that's why there were these standards like PC100 etc. to avoid this kind of stuff...
I took the info from Crucial and searched for RAM that had the same info. And it didn't talk about registered or unbuffered or dual rank.

leew: The board supports both ECC and non-ECC - that much I know because there is a BIOS setting to enable ECC if the RAM supports it.

I went to the Crucial site because we order from them at work, and I knew they had a system scanner - I'll look at Kingston's site to see if they have one, too. Kingston seems to be cheaper and wider available, but still decent quality. But it's old RAM, so I may have a hard time finding it.

Anyway, thanks for your help!
Lee W, MVPTechnology and Business Process AdvisorCommented:
I never said the board wouldn't support both - just that it wouldn't support LARGE sticks of RAM in NON-ECC mode.  Gary may be right, but don't misunderstand what I said.
semmelbroeselAuthor Commented:
leew: I was trying to give you points, too, but I am new to EE, and I didn't see the button "split points" until it was too late... I asked for help by the moderators in the community forum, and I hope someone can do that for me.
Gary CaseRetiredCommented:
If you posted a note in CS they'll re-open the question for you and you can split the points as you choose.   There's no question that you can use 1GB of non-ECC memory -- I've got a 440BX system with exactly that configuration.   As I noted earlier, it's just a matter of having the correct rank structure on the modules.
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