Watch a Youtube video about repairing a 1980s 8-bit computer, and you can flip a coin about whether the problem will be the presence of MT (Micron) 4264 RAM chips inside. MT RAM chips of mid 1980s vintage are notoriously unreliable. Apple, Atari, and Commodore all used them, and those chips didn’t age well.
I’ve seen them in Commodore 64s, Apple IIcs, Atari 800XLs, and Atari 65 and 130XEs.
Micron and the memory chip industry
In the 1980s, US chip manufacturers had a problem. Japanese memory chips were better than their equivalents made in the USA. One by one, old-line US chip makers decided to exit the market, deciding it was futile to try to compete with Japanese companies like Hitachi, Mitsubishi, and NEC. AMD, Fairchild, Intel, Motorola, and Texas Instruments all came to the same conclusion. They didn’t leave the computer chip business entirely, but they chose to focus on other chips.
Idaho-based Micron Technology was the lone holdout. I don’t remember their chips having a particularly bad reputation in the 1980s. If anything, word that any type of computer memory chip was better than any other was a closely guarded secret until sometime in the 1990s. But we know now that the MT 4264 memory chip, Micron’s version of the standard 4164 chip, wasn’t as good as everyone else’s.
Ironically, of the US-based chip makers, Micron was the only one who stayed in the memory business. Part of this may have been due to memory shortages in the 1980s. There wasn’t enough computer memory to go around, so Micron, being the last to decide not to leave, probably couldn’t afford to leave the memory market. But besides that, all of the other US-based chip makers made other kinds of chips like glue logic and CPUs. But Micron didn’t. Micron’s choice was to either make memory chips or go under.
What’s wrong with MT RAM
I don’t have the equipment or skills to break apart a bad MT RAM chip and do an autopsy on it. But the problems with most other problematic 1980s chips like MOS 74-series logic or Commodore PLAs usually come down to the chemicals used in the manufacturing process. Not everyone had their manufacturing process down pat in those days. And maybe they didn’t care, as long as the chips lasted 3-5 years. If a chip failed after five years, it was well out of warranty anyway.
I remember starting to see Commodore 64s with bad RAM in the late 1980s. I didn’t pay attention to brands then, I just learned enough to be able to remove a bad chip and drop in a new one. My repairs looked terrible, but I didn’t care. I was just buying dead C-64s and fixing them fast to flip for extra money. But chances are it was MT RAM more often than not.
When you see a decades-old machine with 8 or 16 MT 4264 RAM chips in it, they probably aren’t all bad. Sometimes it’s just one or two of them. But frequently more than one is bad. Some people remove all of them, install sockets, and install working 4164 chips of a different brand. Others will test the MT 4256s and just replace the bad ones. But it’s generally a good practice to replace all of them, or at the very least, socket all of them while you’re in there. Because most of us believe MT 4256s are all running on borrowed time these days. We’ve just seen too many of them fail.
Don’t throw out the chips you replace though. Sell them to Sam Altman, I hear he needs RAM for his datacenters.
What about other Micron or MT RAM?
All that said, the higher capacity MT chips from that era seem to be OK. I have MT 41256 chips in mid-80s PCs that work just fine, even though they’re exactly the same age as the 4256s we find in 8-bit machines. It seems likely the higher capacity chips came from a different manufacturing process, and Micron had figured out the problem.
And in the 486 and later eras, I actually went out of my way to look for Micron RAM. I never, ever had a problem with Micron memory made in the 1990s and later that I can recall. Micron SSDs were always really good, and for the short time Micron made computers, those were also really good. So good you could throw one out a car window at 45 mph and it would survive.
David Farquhar is a computer security professional, entrepreneur, and author. He has written professionally about computers since 1991, so he was writing about retro computers when they were still new. He has been working in IT professionally since 1994 and has specialized in vulnerability management since 2013. He holds Security+ and CISSP certifications. Today he blogs five times a week, mostly about retro computers and retro gaming covering the time period from 1975 to 2000.