Killingbeans wrote on 2025-11-06, 23:27:

Hi, first post, so bear with me :) […]
Show full quote

Hi, first post, so bear with me 😀

I've been rekindling my love for old PC hardware lately, and obviously that also leads to buying mystery boxes from the local equivalents of Craigslist.

One of my purchases was a €30 crate full of hundreds of random RAM sticks. Mostly 30 and 72 -pin EDO/FPM.

I've been able to sort the vast majority into types and sizes, but some of them are not making it easy.

The attachment is a pic of a particularly mysterious (to me at least) set of 30-pin SIMMs.

I assume they are 4MB sticks judging by the memory chips, but the auxiliary chips have me stumped. I can't find any info on them, but it's very possible that I'm simply looking all the wrong places.

Anywho, in the matters of old hardware, all roads seem to lead to Vogons, and therefore I'm now asking you guys for help.

Sorry if this a dreadfully trivial question, but everything older than socket 7 is almost completely new territory to me.

Are these SIMMs an early example of actual ECC rather than simple parity? Or is something completly different going on?

So these days I repaired a 486, and I added to the 4 MB of 30 PINs, another 4 MB, reaching a total of 8 MB.
Looking at your strange modules, I would say that they are clearly RAMs with 2 memory chips, a parity chip, and the last chip the square one, it could be an ECC chip, but I've never seen any, so I'd say I can't be sure.
As for the capacity, Maybe 4 MB RAM, for safety I don't recommend trying them on a PC, if you want to increase the total RAM, you should first see what SIMM is now, that is, with how many chips, I don't think it's a good idea to mix 2-chip modules with 2+1 or 8 or 8+1 modules.

OKI was a BIG manufacturer of printers. i'd wager 10:1 these are memory simms made for one of their special printers. maybe for a first gen laser. Upgradeable ram was "common" for the first few years of laser printers.

Dulogic 4100g no publicly available datasheet

Sounds like proprietary memory

luckybob wrote on 2025-11-07, 03:21:

OKI was a BIG manufacturer of printers. i'd wager 10:1 these are memory simms made for one of their special printers. maybe for a first gen laser. Upgradeable ram was "common" for the first few years of laser printers.

Makes sense. Guess I'll just keep them as a curiosity and avoid putting them in a system.

The big memory chips are 2M x 8 chips. This means a single chip is already able to provide the required 8 bit bus width of that module. Typically, 4M modules are built from two 4M x 4 chips, which are way more common than 2M x 8 chips, and it's easy to combine two of those to get 4M x 8 without any external logic, while the combination of two 2M x 8 chips requires a decoder that uses an address bit to choose which chip to select.

The SOJ 26/24 package of the smaller chip makes it looks likely that this chip is a 4M x 4 chip. The usual parity chip of a 4MB SIMM would be a 4M x 1 chip, which would be in a SOJ 26/20 package (same size, but more "missing" pins in the center).

My rough guess about this module is that I wouldn't count on it being compatible with 30-pin PC SIMMs at all, and furthermore that it likely tries to interleave two 2M x 8 chips to provide higher burst rates, and the OKI chip on the left is a CPLD that manages the interleaving. The parity chip is used as 2M x 2 (half of the rows and half of the data bits unused), with one data bit being assigned to the left 2M x 8 chip, and another data bit assigned to the right one. It could be a completely different design as well.