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Saturday, October 26, 2013

Memory - Making 128mb SIMMs from 64s

I've been wondering, for several years. If this could be done, myself. But, not having the experience, to know if there was much of a chance of it succeeding. I never tired it. But, this guy, over at did it!:) He put together some old PC Memory and Made 128mb SIMMs from 64s. Check out how...


Making 128mb SIMMs from 64s

Here we are, back with another project that would have been much more useful if I had undertaken it 15 years earlier.

If it's not already abundantly clear, I spend quite a lot of my time working with old computers. I do it for The Hackery, I do it for other collectors, and I do it for fun. But given that most of the stuff I'm working with is a minimum of 10 years obsolete, it can be quite the challenge to source the needed parts. Sometimes that means I have to make my own, as is the case today.


One of the joys of working at the Hackery is getting access to weird and wonderful things which people donate for recycling. Today's project, like many of mine, was inspired by one such donation. Amongst a load of gear from a point of sales company was a large antistatic bag filled with 64 megabyte 72 pin RAM SIMMs. For the uninitiated, this was the standard RAM used by PCs, Macs, Amigas, etc, through most of the '90s. And though sticks as large as 128mb exist, anything beyond 32 is vastly harder to find. So I was quite happy to get enough 64s to keep me stocked into the foreseeable future.


But then I noticed something interesting about the sticks. Though there were only memory chips on one side of the stick, both sides had solder pads. This suggested to me that the stick was wired to support up to 128mb. Given how rare 128mb sticks are, this was an exciting thought. And with so many to play with, it would be no great loss if I broke a few testing this theory. So that's what I did.

To start with I sorted them all out. There were two types, ones with Micron chips and ones with Spec Tek chips. I started with a pair of Micron-based sticks. From there I looked up the datasheets for the RAM chips and the little voltage regulator in the center. The datasheets told me that these were EDO chips, 4K refresh. It also said they ran at 3.3v, which explained the onboard regulator. Most computers which used 72 pin simms ran at 5v. Now, running 3.3v chips in a 5v system isn't ideal, even with a voltage regulator, because the IO voltages will still be a little bit off-spec. This is probably why the Micron-based sticks are actually wired to get ~4.1v from the regulator instead of 3.3v. Again, a bit hokey, but they worked in all the machines I tested them in, so I went ahead.


Memory - Making 128mb SIMMs from 64s

Making 128MB SIMMs From Junk
Making 128mb SIMMs
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