Making 128MB SIMMs From Junk


Working for a tech repair/recycling center, [Jax] has access to a ton of cool hardware. Most of it is junk, but that’s just the way he likes it. Among his better finds in the depths of a tech treasure trove is a huge antistatic bag of 64 MB 72 pin SIMMs. These were the standard RAM form factor for just about everything in the 90s, and while 64 MB is a huge amount of RAM for the time, they’re still a bit away from the 72 pin max of 128 MB.

After inspecting these sticks, [Jax] noticed something odd. Each side had pads for memory chips, but only one side was populated. Given the rarity of 128 MB sticks of RAM, [Jax] decided he would have a go at adding 64 Megs of RAM to these chips by desoldering one stick and sticking it on the back of another.

These new 128 MB SIMMs made their way into a Macintosh Quadra 605 for testing. While the 64 MB chips worked fine, the new 128 MB chips threw a chime of death. Something was terribly wrong.

While investigating, [Jax] couldn’t find any bridged solder joints, and everything looked okay. Heat is a wonderful test of what went wrong, and with the SIMM connected to a power source, he found all of the newly transplanted chips were hot. Because the chips on back side of the SIMMs were meant to be installed upside down, [Jax] had inadvertently connected the ground to power and power to ground.

Fixing his mistake on a new SIMM, [Jax] popped it in his old Mac and tried booting with these SIMMs again. There wasn’t a chime of death, but booting with these chips took a very long time. This was actually just the Mac checking all the RAM, which was successfully addressed once [Jax] finally booted his OS.

25 thoughts on “Making 128MB SIMMs From Junk

  1. I have done half a dozen or so DIMM upgrades. Most of the older memory
    PC133 128MB have double sided footprints for 256MB, but only have the
    top side installed. It is a matter of carefully desoldering SDRAM from
    donator DIMM and solder them onto the back side. If there are decoupling
    caps, series resistor footprints, I’ll fill them in.

    Spend sometime inspecting the solder joints under a magnifying glass and
    watch out for shorts/cold joints.

    1. Always imagined that even if it detects and uses the extra RAM that the timings and voltage in the SPD would be a problem. Seems like these wouldn’t scale with the amount of chips considering what it is they control.

      1. I’d think one lot of chips from the same era are gonna be the same as any other. In this case 64Mb chips. They should all work fine with the same standard timings. Overclocking might annoy them a bit, but I’d bet most SPD chips, on SIMMs of the same size and chip count, contain exactly the same data, or almost exactly.

        The SPD’s just a little EEPROM with the specs in, right?

      2. Back in the SDRAM SDR days, they don’t play the game of boosting the
        voltage of memory modules to “improve” their speeds. Not sure where your
        voltage part comes in.

        If you are soldering the chips from same or better “brands” onto a
        lesser one, then there should not be an issue since you are using the
        less optimized timing there.

        Your memory timing margins will be reduced when you are driving twice
        the amount of loads. The granularity of overclocking in the era wasn’t
        that great to see a difference anyways. Even if you have to reduce
        amount of overclocking etc., your system level performance would still
        improve with the extra memory.

  2. Somebody needs to learn the difference between ‘B’ and ‘b’. If those chips were in fact 64MB, then you’d only need 2 to max out the 128MB of 72 pin SIMMs. But since they’re really 64Mb DRAM chips, you need 8 chips on the front and 8 chips on the back of the 72 pin SIMMs to max them out.

        1. What’s that, the sound of air whistling between your ears as you sit in your parents’ basement, clad in the requisite fedora and neckbeard, so high from smug self-superiority and huffing your own farts, and so autistic that you’re unable to use cues like “context” to realize that when they said “64MB chips” and “128MB chips”, they had meant to simply say “64MB SIMMs” and “128MB SIMMs”?

          Oh, oh, and to top it off, once someone explained to you what the HaD editors meant, you felt the need to try to scrabble ineffectually up onto your high horse and regain a bit of dignity by implying that it was the *other* guy who completely missed the point? Who the hell are you trying to fool?

          Well done, dude, you win Autist Of The Year 2013, and hell, the year isn’t even over yet. Everyone is in awe of your spooky Pedant Powers. Now please, fuck off, and never come back.

        2. People complain about the haters, but at least they contribute something to the discussion.

          The pedant and grammar nazi are a waste of bandwidth.

          (Correcting errors isn’t being pedantic, correcting errors when the context makes it clear what it is supposed it be is.)

          1. @mikemac You are right, units matter (if you check the original page, then they are even talking about millibits). Now when is done, you actually can do it more politely.

            Instead of attacking “somebody needs to learn…” (that references your attitude) you could say something like “I would like to note that probably ….”, or “SIMMs of these days were usually 4 megabytes in size so likely theses numbers here are in megabits (Mb) and not in megabytes (MB).”, or something along that.

          2. Sure units matter, so does context.

            In the case of “well you’re wrong but I know what you mean” there’s no reason to mention it. No-one talks about bits when referring to modules, well, apart from the occasional pedantic dickhead.

            For example, you are wrong but we know what you mean. Therefore this entire comment was as pointless as yours.

          3. KIDS! – SIT DOWN AND BEHAVE! Your mother has a HEADACHE!

            You want to go to Disney World? – Then DON’T MAKE ME TURN THIS CAR ‘ROUND!!

            You know that old meme “arguing on the internet is like….” – Yeah…that.

          4. Please stop using “hater”. It’s one of those words that can mean anything the user wants it to, making the “hater” inquestion seem wrong without any argument or reason. Is it bad to hate… sorry, “be a hater” of war criminals? Or child molesters?

            As well as being doublespeak, it’s bordering on the illiterate, and certainly inarticulate. Put a bit of thought into your language. Be specific as to who you’re criticising and why.

            I know it’s probably pointless but I like to build little bulwarks against the decline of civilisation every now and then.

          5. Units do matter, mikemac, but he used the right one: MB. When he said chip, he obviously meant SIMM and not the individual chips soldered onto it, which was pretty obvious. Now, is it a shade ambiguous? Yeah, maybe, it is. And so it’s not out of line to point it out. But when you start with “Somebody needs to learn…” you’re being disrespectful. There’s nothing in the original wording that indicates he doesn’t know the difference between Mb and MB.

          6. There are no ‘haters’ in this thread in the sense it is used by Hackaday comment writers.

            Look everyone, context again.

            What we do have is boring people like mikemac who you avoid at parties.

  3. >Kris Lee says:
    >October 26, 2013 at 1:19 am
    >@mikemac You are right, units matter (if you check the original page, then they are
    >even talking about millibits). Now when is done, you actually can do it more politely.

    Kris, you are correct. I could have and should have been clearer and more sensitive in my original response. In my attempt to be brief and not start a flame war, I did just the opposite. I’ll try to do better in the future.

    I, me, myself, I DID find the description extremely confusing. I had to reread it several times before I could figure out what Jax was doing. I couldn’t figure out why he was trying to an extra 512 megabytes on the back of the SIMM if the SIMM had a 128 megabyte limit. It was only after I finally realized that the description meant 64 megabits and not the stated 64 megabytes did it make any sense. Maybe I was in a too literal state of mind or maybe I was mislead because I remember DRAM chips did come in both x1 and x8 configurations. But whatever the reason, I will try to be clearer in the future.

    1. I appreciate your response. It is very easy to be mean in Internet when you try to be brief.

      I did not really bother about the actual values. What I took from this piece of information was that early memory cards had only one side populated with chips and you were able to double the capacity by soldering the chips by yourself.

      I think that this is a cool hack and may give an idea to somebody who loves to mess around with old hardware.

    2. How could you possibly get the values wrong when only two numbers are ever mentioned – 64 & 128.

      Only top of that the units are blatantly obvious – to double the capacity of a 64 meg SIMM you need to add another 64 meg.

      Accidentally writing mb, mB, Mb or MB does matter – the context makes it clear.


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