August 4, 2026
When storage meant tiny arson
Looking inside a 1970s PROM chip that stores data in microscopic fuses (2019)
Inside the chip that saved data by literally burning tiny links — and commenters are losing it
TLDR: This 1970s chip stored data by permanently burning microscopic links, a reminder of how physical early computing really was. Commenters turned that fact into the main event, joking about "magic smoke," sharing painful swap-out stories, and arguing that this old tech didn’t disappear as quickly as the article suggests.
A deep dive into a 1970s memory chip should have been a quiet nerdy museum moment. Instead, the comments turned it into a full-blown nostalgia party, complete with magic fairies, repair horror stories, and a low-key fight over what really replaced these old parts. The chip itself is wonderfully wild by modern standards: it stored just 1,024 bits, cost about $70, and saved information by blowing microscopic fuses inside the chip. In plain English, you wrote data once by burning tiny links, and that was that forever.
The community absolutely ran with the drama of that idea. One commenter joked about the "magic fairy smoke" escaping from electronics, while another casually dropped the sort of sentence that makes modern engineers sweat: they used cheaper one-time chips in production, then desoldered and replaced all of them if a bug showed up. That was the mood everywhere — half awe, half "you kids have no idea how brutal old hardware was."
The spiciest mini-debate came from the history buffs. The article says these chips were overtaken in the 1980s by erasable versions, but commenters rushed in with a classic internet correction: well, actually, not in every corner of electronics. Translation: the old fuse-burning approach hung around longer than you might think. So yes, the microscope photos are cool — but the real show is the comment section, where engineers are reminiscing about an era when programming a chip was basically tiny, controlled destruction.
Key Points
- •The MMI 5300 was an early-1970s PROM that stored 1024 bits as 256 words of 4 bits and originally cost $70.
- •The chip was one-time programmable: intact Nichrome fuses represented 1s, and users programmed 0s by blowing selected fuses with high voltage.
- •Microscope analysis showed the memory cells arranged as a 33×33 array of diodes and fuses, while most of the die area was devoted to support circuitry.
- •The fuse elements were about 8 µm long, and a blown fuse produced a crack roughly 700 nm wide rather than disappearing completely.
- •The PROM used a two-stage addressing scheme in which A3–A7 selected columns and A0–A2 controlled multiplexers, with column decoding implemented using NAND gates and multiple-emitter transistors.