November 5, 2025
Ancient chips, fresh drama
A Lost IBM PC/at Model? Analyzing a Newfound Old Bios
Mystery IBM chips spark nostalgia, snark, and a hunt for a forgotten PC legend
TLDR: Newly found IBM chips include an earlier PS/2 firmware and a mysterious PC/AT-era BIOS that doesn’t match any known release. Commenters debated AT/370 vs prototype, mixing nostalgia with dot-label jokes—showing why saving old ROMs matters for piecing together tech history.
A pair of mysterious IBM chips landed on a vintage forum, and suddenly the retro crowd was in full detective mode. The “starter software” inside these chips (the BIOS) is what wakes a computer up, and one set turned out to be an earlier-than-known PS/2 edition—Major Tom and the Ardent Tool crew tagged it and put it online. The other set? A tantalizing 1980s IBM PC/AT-era brain that doesn’t match any known versions, sending sleuths into archives like Minus Zero Degrees and PC DOS Retro.
Cue the comments: mrlonglong cheers the write-up, while drfuchs throws shade with a spicy guess—maybe it’s for the “nobody used” AT/370. That single jab kicked off the central debate: lost model versus obscure prototype, with fans defending IBM’s forgotten side quests. eek2121 brings heartfelt nostalgia—“I would’ve gone down this rabbit hole”—a vibe echoed by many who grew up on repair manuals and message boards. And yes, the thread devolved into micro-obsession humor when sema4hacker demanded label symmetry: ..ODD.. vs .ODD... Suddenly, the dot drama became the meme of the day. The mood? A perfect blend of curiosity, roast-level snark, and retro love—exactly what happens when ancient silicon meets modern internet energy.
Key Points
- •Two IBM-labeled EPROM pairs were found and dumped; one dated “25/05/90” and another marked “© IBM CORP 1981,1985.”
- •The “25/05/90” pair was identified as PS/2 Model 35/40 SX BIOS revision 2 and is now archived on Ardent Tool’s System ROMs page.
- •The “1981,1985” EPROMs contain a model byte FCh and odd/even interleaving indicating an IBM 5170 (PC/AT) 16-bit architecture.
- •Despite these indicators, the “1981,1985” EPROMs’ dates, part numbers, and contents do not match any of the three official IBM 5170 BIOS revisions.
- •The article reviews official PC/AT BIOS revisions and sources (Minus Zero Degrees, PC DOS Retro, Ralf Brown’s Interrupt List) used to compare and identify firmware.