well, its entirely possible its for the IBM series.

it seems you are handy with a multi meter. I would ring out the SPD pins at the far end of the simm. if it matches with the table at the bottom of this site: https://www.ardent-tool.com/memory/Reference.html then its a very good chance its for IBM machines. If not... it could be for IBM, but quite a few printers had memory upgrades that used 72 pin simms. 16mb would be HIGHLY unlikely.

my guess is IBM PS/2 (for example P70)

Actually this fits with what I see with these incompatible 4MB SIMMs made by IBM I have were actually made for late models PS/2 that uses 4MB simms including 90 XP. Which was confirmed by looking into IBM parts catalog to find out what PS/2 uses them.

Chips array used on it is also unusual. 9 x 4 bits chips for 36 bits all identical, that's parity simms.

Cheers,

9 chips just means its parity. the space for a 10th just SCREAMS ECC ram which was pretty much exclusive to the 859x ibm machines. or other similar machines

luckybob wrote on 2023-09-16, 22:33:

well, its entirely possible its for the IBM series.

it seems you are handy with a multi meter. I would ring out the SPD pins at the far end of the simm. if it matches with the table at the bottom of this site: https://www.ardent-tool.com/memory/Reference.html then its a very good chance its for IBM machines. If not... it could be for IBM, but quite a few printers had memory upgrades that used 72 pin simms. 16mb would be HIGHLY unlikely.

I've tested the complete pinout of these modules and can confirm that module schematic is 100% compatible with ECC SIMM described in the table II here:
https://patentimages.storage.googleapis.com/6 … 6/US5375084.pdf

However:
Line 11 (PD5) is connected to two non-populated resistors which can connect it with A10 or GND
U9 (the 10th DRAM chip) is not populated, so lines 64-66 and 71 are N. C. but for some reason, there is non-populated resistor which could connect line 71 with A11 (???)
PD lines are correct for 16< 60ns module (e.g. 67 is tied to GND)

So, it looks like a Frankenstein 36-bit ECC. And you think, PS/2 is the only type of computer which can utilize it?

i'm 95% confident it is for the IBM series. probably only for the 90, 95, or pc server 500 models.

Did you want to let them go? ^.^

ECC is not 36 bits, that's parity for consumer computers most of time that is industry standards that sticks to if the four CAS lines are all different, each of CAS line connects to 8 or 9 bits wide sub-banks. The required bits for ECC to function to correct is 7 bit extra on top of 32bits. I have seen 39 bits ECC and 40bits modules as well as it is completely different pinout in 72 pin form factor.

Also the specs pinout for 72 pins SIMMs does indicates the required pins used for ECC are not the ones for parity.

Specially designed SIMMs with 36 bits like this you have is usually paired or quad SIMM as a bank for ECC function to work and this is only found on special machines only have one CAS or two tied to all the identical ICs.

True ECC simms pinout is in this link. Two CAS lines.
http://www.interfacebus.com/Memory_Module_72P … IMM_PinOut.html

Link is this is consumer parity simm. Does not match your either. This requires 4 sub banks of 8 or 9 bits each each one CAS line. Like this is each CAS line is tied to 8 bit data either with or without parity bit. Or a special quad CAS IC on one die. What it looks like for each CAS line is SIMM with identical 4 bit by 8 chips or 9th chip not identical to rest as it is now 1 bit for parity. Another is 3 chip, with 2 is identical IC and one IC with 4 cas single IC.
http://www.interfacebus.com/Memory_Modules_72 … IMM_PinOut.html

Cheers,

luckybob wrote on 2023-09-18, 18:17:

i'm 95% confident it is for the IBM series. probably only for the 90, 95, or pc server 500 models.

Did you want to let them go? ^.^

Currently I just have to decide what to do next with them. Having no access to these specific machines I can't find out if modules are actually working so couldn't sell them for a reasonable price. On the other hand, it's 63x 4Mx4 60ns chips perfect for brewing DIY modules for 386 machines.

Some Cisco routers (2500 etc) used 72pin parity simms, maybe they also supported weird configurations.

IBM PS/2 SIMMs work in allmost any other Motherboard, as they are just ordinary SIMMs with parity andpresence detect.
Even the ECC SIMMs that can be easily recognized by the presence of the two square chips visible as EOS Simms at
https://www.vogonswiki.com/index.php/72-pin_SIMM wor in othe machines.
The 40 Bit ECC are usually from RS/6000 Series 7012 , 7013 and 7015 where 8 of these sit on a memory board with some logic circuitry.
Other proprietary SIMMs can originate from HP 9000 series.
Even between different series of machines different SIMMs are used.
Modules from an E45 did not work in a 712, 715, B- or C-Class HP 9000.
These can sometimes be recognized by manufacturer part Nos, but third party modules for these machines are difficult to recognize.