I have an unusual problem. Okay, so some of us have more money than brains (or little of either). Since I received such fantastic assistance with my ThinkPad 600x (now at 576MB, 60 GB hard disk with three operating systems) maybe someone can help me with this problem on an IntelliStation mPro (6850-65U). Over the years I have added RDRAM until all of the slots (8 in total) have been filled. Each slot has a 512 MB RIMM. This should give me 4096 MB of RAM. Until I replaced the last two RIMM (256 MB with 512 MB ones) I had 3584 MB (6 x 512 MB plus 2 x 256 MB).

Now with all slots at 512 MB, I seem to be missing 512 MB? Diagnostics shows everything is okay; Belarc Advisor Profile indicates all eight RIMM's are 512 MB, yet it shows a total of 3584 installed memory, not the 4096 MB expected. Where has it gone?

If you interrupt the boot and go into the BIOS set-up program, how much RAM is shown there?

Sorry for the delay in responding. There are six of us using this machine (kids and wife) so I cannot always respond when I want.

POST indicates 3,670,016K RAM (which is consistent with BelArc). When I replaced two other RDRAM with my original 256 MB, it shows 3584 MB installed memory. This indicates that the new RDRAM are fully functioning (consistent with the diagnostics). So if I use six 512 MB and two 256 MB I get 3584 MB, and when I use all eight 512 MB I still get 3584 MB. Of course, because this is an old machine, IBM no longer provides free support.

So I repeat, where is the missing 512 MB (or so) RAM? (Interesting problem, isn't this?)

If it were me, I would take out all but 4 of the 512s, verify that all is OK. Then I would add the two new 512s (don't put in the 256s) and verify that the new 512s are OK using this method.

If that checks out OK, I would get a program like CPU-Z or something that will show you the specific timings of each stick of RAM. I think RDRAM is very sensitive to having parts that are exactly matched.

I would check to make sure you have the latest BIOS. I have heard of some machines (not IBMs) that require a BIOS update for larger amounts of RDRAM.

If still no good, I would try swapping the sticks around into different sockets.

If that doesn't work, I personally would probably give up, and console myself with the fact that 32-bit versions of Windows can't support all 4G anyway.

I have already tried that (I guess my explanation above is not the clearest - blame it on old age.) If I use two or four or six sticks, the amount is correct. It does not matter which pair I used, the total was always 1 GB (or 2 GB or 3 GB). It is only when I use all eight sticks of 512 MB that the anomaly appears. I will try CPU-Z after I find it.

The sticks have been switched around so much, that I do not think that is the problem. Finally, the BIOS is up to date (my next step is to install a second processor.) Other than for the "missing" RAM, the machine seems to be working. The only question that intrigues me is the statement that 32-bit versions of Windows can't support 4G. Does anyone have more info on this. My version of Windows is XP Pro (SP3) - the 32-bit version.

I think you can research that on this board. I don't remember the exact details. But that's the reason I asked what the machine's BIOS reports. The BIOS is not affected by operating system limitations, so it should report the "full" amount even if Windows cannot.

I'm assuming that all the sticks are the same with respect to parity checking and buffering... ?? If they all match, then I am stumped at this point in time.

I would be leaning toward slight differences in timings on the various sticks of RDRAM, but that's just short of a pure guess on my part.

Thanks for all the help. If anyone can think of any other possibility, please feel free to contribute. I am also leaning toward the probability there is a timing problem with the RDRAM. However I will live with it.

One thing I will experiment with is to try the sticks (2 by 2) and check under BIOS as well as under Windows. Maybe it was because I used several different brands of RDRAM, still it did not seem to matter which pair I put in last; the last pair always gave me the same anomaly.

So once again, thank you for your help with my old machine.

Hi. I know this is probably something you're not even looking at now; however, just in case you are...

There were some Intel chipsets that required a larger reserved memory area when installed memory == 4GB. It would never report 4GB, no matter what. This sounds very much like that. I don't know off the top of my head which chipset is in that model of MPro, but this may be a possibility.

Now, I may be way off here, too, because I don't remember if this affected only dual processor (way back then when there was only one core per socket ) or if it also affected uni-processor models as well. I know we ran into it a lot with some of the xSeries servers a few years back -- customers would complain that they were missing 512MB of memory, but the system actually reserved it (and I can't remember what for, exactly... adapter BIOS shadowing? I don't remember; sorry).

Anyway, FWIW, I thought I might throw that out at you. I have a little experience in this area, being that I work for IBM in the x86 server and professional workstation side -- when we still had them.

Hope this helps.

Tony

Home machines: Thinkpad T43 2668-44U; Intellistation ZPro 9228-72U, and the 2645s that will never die
Work machine: Thinkpad T61 7659-A71

Thank you to all for help and suggestions. In case anyone else runs into the same problem, I have posted the following link: Why can't I see all of the 4GB of RAM in my machine?. This page gave the shortest answer. With 4096 MBytes installed, Windows XP 32 bit version cannot address anything higher than 4 GB.

After posting for help here I looked at other resources. Windows XP magazine from the United Kingdom had someone else listing much the same problem as I had. Their explanation was good, so I thought I would Google it and post it here.
Memory Map
So again, thank you. Hopefully this will help someone else.

You could try some Linux LiveCD (like Ubuntu) to see whether it can utilize all 4 GB of RAM as most recent distros come with PAE included and enabled per default (provided your chipset supports PAE). If your cpu supports x64, you could even try 64-bit Linux LiveCD. (BTW, I´m not aware of a single case where PAE in XP improved anything...)

Not to say something strange, but ibm xSeries servers state clearly in the HMM that if you install 4 or more gb of ram, part of it will not be available but instead used by the bios for internal pci things.

I remember the intellistation z pro to have the same thing in the manual... so I would suppose this extends also to the m pro, even if I've not checked the appropriate hmm, but would make sense since it's a workstation class machine like the z pro.
In this case the os has nothing to do with the missing memory, but instead is simply a feature of the bios implemented by IBM.