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I have recently acquired an Atari 1040 STe with 1MB of RAM.

I read that you can extend its RAM with 30 pin SIMM up to 4MB. But it can be done only with 256KB or 1MB SIMM, and that 2MB, 4MB, 8MB and 16MB SIMM should not be used.

I have 6 30 pin SIMM but there are no stickers on them that tell me their size.

I have 2 models:

  • 4 ones with 9 vertical chips marked "OKI Japan, M514100B-70SJ, 40222539A9Z", and there is written on the back of the modules "MSC23409B-70DS9 4041001, JAPAN";
  • 2 ones with 3 horizontal chips marked "JAPAN A014, 9236 65NT, HM514400AS7", and there is written on the back of the modules "HB56G19B-7A, 9242 TT 13".

I don't want to damage my Atari 1040 STe by using modules with the wrong size, so how can I identify the size of 30 pin SIMM with those informations?

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To identify SIMM sizes based on chip IDs, search the Internet for the chip IDs to see what each chip is (chip datasheets are a good way to find this out), then multiply the chip capacity by the number of chips.

For example, an M514100D (D probably is a newer version but otherwise compatible with M514100B) is a 4Mbit x 1 fast page mode DRAM chip. So if you have a module with 9, that is probably a 4Mbit x 9 FPM DRAM module (aka 4MByte with parity).

An HM514400 is a 1Mbit x 4 DRAM, so 3 chips would make 1Mbit x 12, so the module is probably 1MByte with parity (9 bits, leaving 3 bits unused/wasted).

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    incidentally, in my experience a module with 3 x4 chips is uncommon due to the wasted bits. I have seen 2 x4 chips plus 1 x1 chip much more frequently, with the x1 chip sometimes being a different size than the other 2. but it's not impossible, I imagine in this case Hitachi had tons of x4 chips lying around so it was cheap for them to just use those for the 9th (parity) bit and disregard the 3 extra wasted bits. if there's another chip on the module it's possible the extra bits are being used to enable some kind of ECC memory.
    – Ken Gober
    Sep 1, 2016 at 15:49

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