Build Your Own 16 MB 30-Pin SIMMs For Vintage PCs

Today’s memory sticks have hundreds of pins and many gigabytes of RAM on board. Decades ago, though, the humble 30-pin SIMM was the state of the art where memory was concerned. If you’ve got vintage gear, you can try and hunt down old RAM, or you can copy [Bits und Bolts] and make your own.

Previously, [Bits und Bolts] built a 4 MB SIMM, but he’s now ramped up to building 16 MB RAM sticks — the largest size supported by the 30-pin standard. That’s a ton compared to most 30-pin sticks from the 1980s, which topped out at a feeble 1 MB.

We get to see four of his 16 MB sticks installed in a 386 motherboard, set up to operate in the appropriate Fast Page Mode. He was able to get the system operating with 64 MB of RAM, an amount still considered acceptable in the early Pentium 3 era. Hilariously, memtest took a full ten hours to complete a single pass with this configuration. [Bits and Bolts] also tried to push the motherboard further, but wasn’t able to get it to POST with over 64 MB of RAM.

As [Bits und Bolts] demonstrates, if you can read a schematic and design a PCB, it’s not that hard to design RAM sticks for many vintage computers. We’ve seen some other RAM hacks in this vein before, too.

28 thoughts on “Build Your Own 16 MB 30-Pin SIMMs For Vintage PCs

    1. That could be the earlier version of this, the timing is about right. This was him finding some donor modules with very large chips and trying to max out his motherboard.

      1. Independent development. Bits und Bolts covered EDO to FPM hack last year after a tip from one of his viewers in comments while making those so he was unaware of this repo solving both problems over 2 years before. Plenty of people on Vogons got surprised by this hack too suggesting there is still problem with disseminating somewhat more obscure esoteric technical vinatge computing knowledge.

  1. I was prepared for memtest to take a little bit longer, but 10 hours for scanning 64MB is ludicrous, what it tested and how it this done. That means that testing RAM is at a speed of less than 2KB per second! That must be some pretty intensive testing.
    Regarding this project, pretty cool project, good to keep these old machines running.

    1. Bitfade is all about letting it sit, then circling back and checking.

      If you’ve ever run into RAM with this problem, you won’t skip it again.
      Just let the basic build sit and run overnight.

  2. Cool project, but I’d bet that hundreds of those old memory sticks hit the junk yards every day. Can’t be that difficult to find some. eBay has several for sale right now for as low as $10 each.

    1. Good luck finding 4 (or more) identical 16MB modules that all work flawlessly… I haven’t checked ebay myself, but I imagine 16MB sticks were always pretty rare. My first PC was a pentium 133MHz and that had a total of 16MB EDO RAM. I remember that 8MB was kind of standard back then. I soon upgraded to 48MB which made a huuuge difference. Also, the motherboard supports up to 256MB which was ludicrous in 1995. I still have that machine in the attic. But it won’t boot due to a depleted backup battery of that built in, non-replaceable type. One day I’ll fix it. Maybe.

    2. And there’s something to be said for being a producer not just a consumer. In other words, having the power to make more on demand instead of waiting to others to chuck theirs out.

  3. Hm. 1 and 4 MB models are more compatible and precious in general, I think.

    4 MB (4×1 MB) often was the limit of early PC motherboard chipsets.
    16 MB (4×4 MB) was limit of ISA bus address range and thus 286 and 386SX PCs.

    64 MB (4×16 MB) is maximum of XMS v2 specification
    and maximum of what OS/2 can address without special BIOS support.

    Such an gigantic amount of RAM used to be nice for high-end 486 workstations and Novell Netware servers.

    The PCs had to have enough cache installed on motherboard, though. 128KB or more, I think.
    Otherwise, the huge memory expansion would slow down the system.

    128 MB (8x 16 MB) is theoretical maximum, if 8 SIMM slots are being available (two 32-Bit banks).
    It’s nice for scientific simulations and high-resolution graphics, 3D rendering etc.
    This used to in the realms of SGI workstations etc.

  4. Just like nowadays most people don’t actually need 64GB of ram

    No video games right now come close to needing that, may half a terabyte for the install and updates

    And a 3-4ghz quad core or better

    With a minimum of 4GB vram

    And minimum of around 8GB system ram

    Enough for 100+fps @ 1080p wit max settings

    1. 64GB -128GB mobo are designed for sever and specialized workloads like parallel bit slicing, that’s
      how supercomputer work, throw 4 and ryzens, with 4 GPU and a memory/io chip for the bandwidth. Then network 1000 mobos in racks over Ethernet and m.2,nvme,or pci-e as a single “desktop”

      That can emulate even PS5 and Xbox one with 20k support and 16xmsaa get like 1000fps

        1. 64GB but what kind of ram

          Ddr3, ddr4, ddr5

          How about 64GB of sram and no CPU wait state, ram runs as fast as CPU cache? But roughly $1000 per GB if you can find someone to make sram, and remove the dram refresh circuits with something more useful

          1. Sram doesn’t need to be constantly reminded of what it needs to remember

            And has faster access times because of its asynchronous nature

    2. for videogame frame rates i imagine you’re correct but…

      i don’t use much ram. when i upgraded from 4GB to 16GB, i thought the 4GB was already comical overkill..i just bought 16GB because it was so cheap, “when in rome”. but then i had a computer with 16GB for a while, and i was typically only using about 2GB out of it. i thought it was hillarious. but then one day i did an operation that flushed the disk cache, and suddenly my PC was *SLOW* while it loaded everything up. even SSD is a lot slower than RAM. and i figured i’d be doing that operation a lot more in the future, and i never want to flush the disk cache again. so i got 32GB of RAM and golly gee it made a big difference.

      so it depends a lot on your usage scenario but if my userspace processes are using 2GB of RAM, with 30GB “free” but used for disk cache, that 30GB isn’t waste, it’s doing me a lot of good. somewhere along the line i simply got used to 99% of my daily files being in RAM at all times. and i never want to go back.

      i don’t need 128GB, but next time i replace my motherboard (i seem to be on a 9 year cycle, so 2028ish), i shouldn’t be surprised if that’s what i wind up with.

  5. To those stating “why not buy them used off ebay (or whatever market)”…
    The larger capacity DIMMs modules were really expensive when they were current technology so few ever purchased them, making them relatively rare and quite expensive. My guess is the CEOs that could afford them tossed them in the trash with their “obsolete” computers. I’ve tried many times to upgrade my older laptops to keep them in service, but the price of larger SODIMMS is crazy. Smaller ones are pennies on the dollar, but high capacity ones are like “hen’s teeth”.
    You can buy current technology modules with 1000x the capacity for much less per megabyte. Since there’s a lot of older equipment that takes the old modules that can’t be replaced and they are rare. That combined with the fact that nobody is manufacturing these old modules any more makes them “precious”. PCBs are cheap, so become the manufacturer, get the old ram from China and you might be able to profit. I’ll be waiting to buy some from you…

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