Also of interest is someone having memory woes:
Memory problems
Lately, I experienced all kind of memory problems (unreproductible gcc internal error, sig 11, random kernel crashes), that suggested me a problem with memory modules. My machine is running with one 1GB SDRAM, I purchased an additionnal memory module from IBM (512MB PC2100, CL2.5, FRU 10K0033, 2003-01-23) to add to the built-in 512MB modules. This module is correctly referenced by IBM, and is supposed to work in my T40.
memtest86 quickly found several memory errors, on test 3 and 4, all addresses locations were above 512MB. Similar errors were found both on battery mode (CPU clocked at 600MHZ), and on AC mode (CPU clocked at full speed at 1600MHz). The errors disappeared when running memtest86 with only the 512MB built-in module. This additionnaly memory module is stamped with an IBM sticker, and memory chipsets come from Micron Technologies (P/N MT16VDDS6464HG-265). Running a full memory test with the shipped PC-Doctor program didn't find anything wrong with both modules. Should I suspect random errors due to overheat ? The back of the laptop, where the memory module is inserted, is not really air cooled, and the module appeared to be rather rather hot, when I removed it to proceed to my investigations. Any similar feedback welcome.
Update 2003/06/14: Some more diagnostics about the memory problems. The memory errors are currently only detected with the memtest86 program. This program is free software, and released under the GNU GPL License. This patch has to be applied on version 3.0, so the cache size of the Pentium M processor is correctly detected by CPUID.
I extracted the builtin memory module of my laptop. The T40 - Hardware Maintenance Manual is of great help to provide useful information about the internal organisation of your laptop. Accessing the builtin memory module requires to remove the keyboard. This operation is relatively easy to achieve. It requires no special screw driver, just a little care for the connection ribbon of the keyboard.
The internal memory module is Infineon chipsets, the spec sheet is not (yet?) available on Infineon's web site (P/N HYS64D64020GBDL-7-B, PC2100S-2033-0-Z, 512MB, DDR, 133MHZ, CL2). So the noticeable difference between both internal and supplementary modules is their Cas Latency (CL).
Running with only the Micron memory chip in the builtin memory slot worked fine with memtest86. No error detected after 4 iterations of the whole tests sequence. It took approx 3 hours to complete these 4 iterations. Then I reinserted the Infineon memory chip back in the supplementary memory slot on the bottom of the machine. I came back to a 1GB configuration and both modules were swapped from their original location. memtest86 found errors in this configuration too.
To sum up, each module works fine separately, and they fail when put together.
* In the manufacturer configuration (infineon CL2 builtin chip, and Micron CL2.5 supplementary chip), all failing addresses are located above 512MB, and after I swapped the chips, the failing addresses are now located below 512MB. So the problem seem to be located on a single module.
* The error-bits pattern given by memtest86 (aka the difference between the bad value and the good value) are very similar for each error : in most cases, 0x000000ff, 0x0000ff00, 0x00ff0000 or 0xff000000.
Problem with a mixing CL ? I'll probably contact IBM very soon to obtain some explanation about this problem. Stay tuned!
Update 2003/06/17: I tested again the supplementary memory module alone. And after a more longer testing period than the previous one (a whole night long), the memtest86 program finally found some errors, after somewhat 9 passes. Not many errors, 40 approximately, all concerning test number 3 and 4. Less errors were found than when both chips were in use. This confirmed my impression that a single memory module is buggy : the supplementary one. I contacted IBM France, and they accepted to change this module after some discussion. For now, I run Linux with the builtin memory only, and I didn't experienced any single failure yet. Quite rassuring.
Update 2003/06/21: I received yesterday my new 512MB memory module FRU: 10K0033, Samsung Chipsets (P/N PC2100S-25330-Z, M470L6423DN0-**0, CL=2.5, date 2003-04-11) and made some tests. The memtester userland program did successfully run several hours long without problem, and the memtest86 program did successfully run during a whole night, 7 passes with defaults tests. I also recompiled without problem the whole GNOME environment from CVS. According to these tests, I can conclude that the memory combination is now suitable for a daily use of this laptop.
