SIMM

4 Articles

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

July 9, 2024 by 28 Comments

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.

Continue reading “Build Your Own 16 MB 30-Pin SIMMs For Vintage PCs” →

Maxing Out Your MacIntosh With A 4 MB Memory Stick Kit

January 12, 2023 by 22 Comments

One fun aspect of retrocomputing is that you get to max out all aspects of these systems without having to take out a bank loan, as tended to be the case when these systems were new. Less fun is that decades after systems like the Apple MacIntosh SE/30 were last sold, the 30-pin SIMMs that form the expandable RAM for these systems has become rather scarce. This has led many to make their own SIMM PCBs, including [Kay Koba] with a PCB for 4 MB SIMMs along with information on which memory and parity ICs are suitable for these SIMMs.

For systems like the MacIntosh SE/30 with 8 30-pin memory slots, the maximum capacity is 128 MB, but this comes with many gotchas due to its ROM being ’32-bit dirty’. While this can be circumvented by swapping in a ROM from a later MacIntosh variant, the less invasive way is to enable the MODE32 system extension and install eight 4 MB SIMMs for a total of 32 MB RAM. RAM chips for such 30-pin SIMMs can be scavenged from the far more common 72-pin SIMMs, along with any old new stock one may come across.

These 4 MB SIMM PCBs are offered for sale by [Kay] with optionally the SMD components (capacitors, resistors and LED) included in the package. The original PCB card edge design is credited to work by [Zane Kaminski] whose GitHub profile also leads to e.g. this 30-pin SIMM project.

Have you modded your MacIntosh or other retro system yet to the maximum RAM and storage limits?

Using SIMMs To Add Some Extra RAM On Your Arduino UNO

April 9, 2014 by 70 Comments

A Single In-line Memory Module (SIMM) is a type of memory module containing Random Access Memory (RAM) which was used in computers from the early 1980s to the late 1990s (think 386, 486, Macintoshs, Atari STE…). [Rafael] just made a little library that allows you to interface these modules to the Atmega328p-based Arduino UNO in order to gain some memory space. His work was actually based on the great Linux on the 8bit ATMEGA168 hack from [Dmitry Grinberg] but some tweaks were required to make it work with [Rapfael]’s SIMM but also to port it to the Arduino platform. The 30-pin SIMM shown above is capable of storing up to (hold on to your chairs…) 16MB but due to limited amount of available IOs on the Atmega328p only 256KB can be used. Our guess it that an SPI / I2C IO extender could lift this limitation. A quick (shaky) video is embedded after the break.

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Making 128MB SIMMs From Junk

October 25, 2013 by 25 Comments

simm

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.