It's probably 1MB with 384KB taken as shadow ram. If your bios has a memory relocation feature, or allows you to disable system & video bios shadowing (or both) it's possible you can recover some or all of that.

jakethompson1 wrote on 2024-11-07, 18:51:

It's probably 1MB with 384KB taken as shadow ram. If your bios has a memory relocation feature, or allows you to disable system & video bios shadowing (or both) it's possible you can recover some or all of that.

Humm that would make more sense actually 😁
I will have a look later. Thanks!

Indeed, a 1 MB stick composed of
8 times M514256 "256 K x 4-Bit Dynamic RAM Low Power 256 K x 4-Bit Dynamic RAM"
and 4 times M51256 "256K x 1-Bit dram" for parity

Maybe was made for a printer as a bottom tier option?

I have read about them in motherboard manuals in the supported memory configuration sections, but never seen one before.

rasz_pl wrote on 2024-11-07, 20:02:

Maybe was made for a printer as a bottom tier option?

Looks like 68X6253 is for compatibility with an IBM part number for a PS/2 Model 80 SIMM or something else of that era, when 1MB per stick was still a lot

I believe that was the first PC to use 72-pin SIMMs long before they were adopted on clone boards?

72 pin SIMMs exists in 1MB, 2MB too. This was found more often in older computers from 1987 era especially IBM PS/2 such as 50z, 70. Compaq at this time was using proprietary plug in memory modules. Clones was using DIP chips and 30 pim simms at this time.

Clones started to use 72 pins when 486 became mainstream along with cheap ones using 30 pins simms.

Cheers,

1MB were defined in presence detect tables https://www.ardent-tool.com/memory/Reference.html Personally I only ever saw 2MB and up.

jakethompson1 wrote on 2024-11-07, 20:28:

Looks like 68X6253 is for compatibility with an IBM part number for a PS/2 Model 80 SIMM or something else of that era, when 1MB per stick was still a lot

I believe that was the first PC to use 72-pin SIMMs long before they were adopted on clone boards?

this is the last variant of model 80 released in 1989 https://www.ardent-tool.com/8580/Planar_T3.html still proprietary 3 by 32 pin mem cards instead of simms https://www.ardent-tool.com/8580/Memory.html

pentiumspeed wrote on 2024-11-08, 00:54:

72 pin SIMMs exists in 1MB, 2MB too. This was found more often in older computers from 1987 era especially IBM PS/2 such as 50z, 70.

PS/2 50z and 70 sound right, both release date June 1988
https://www.ardent-tool.com/8550/Planar_Z.html
>ZM45 72-pin SIMM slot
>Memory Uses 85 ns 1 or 2 MB SIMMs (1 slot on the planar).

https://www.ardent-tool.com/8570/Planar_T1.html
>J30-32 72-pin SIMM socket

I cant find any IBMs from 1987 with 72pin Simm slots, 1988 might be the date.

AcerPower 386 PCs used 72pin SIMMS as well (1992).

4x 4MB SIMMS were the max, but 1MB would not be out of place.

My NCR MCA system came with 4x 1MB simms

in 1987 model 80 used plug in large memory modules. early 50 and 60 used proprietary 30 pin four simms, while later on, model 50Z came with 1 72 pin SIMM replaced the early 50.

Thank you, that correct model 70 came out in 1988 and later.

Cheers,

Wow, so much knowledge! Thank you all for the replies.

I never knew 386's with 72 pin slots were a thing. 😮

Later on during early to mid 1990's, some late 386 boards such as SBC cards use this and Compaq for example Deskpro/M uses 8 slot 72pin SIMMs expansion card in addition to the standard 4MB/8MB/16MB depending on processor card.

Cheers,

jonesmacarrones wrote on 2024-11-08, 19:52:

Wow, so much knowledge! Thank you all for the replies.

I never knew 386's with 72 pin slots were a thing. 😮

I had a 286-25 with 72 pin simms.

1mb 72pin is rare but not unheard of early on.

2mb simms were extremely common “back in the day” and were the only way to have 4mb in a pentium (assuming they didn’t just solder memory to the board.)

What I find odd is the computer repair place I hung around at mid 90’s had thousands of 2mb 72 pin simms in a pile from upgrading machines circa -1995.

God only knows what happened to these once common things because despite dealing with the tear down of thousands of systems I never saw them after 1997 and only have one left from a Compaq 386sx

It’s almost like all the baby 72pin simms got scrapped after being upgraded out of.