this repository For the disassembled code and the ROM images discussed here, see
Something intriguing turned up recently over at the Vintage Computer Federation Forums. Member GearTechWolf occasionally rescues and dumps random ROM chips that show up on eBay, and makes the contents available so they aren't lost to the ages. One of his hauls turned up two pairs of EPROMs labeled "IBM" in plain dot- matrix: one showing part numbers (and "© IBM CORP 1981,1985"), the other tagged with a specific date ("25/05/90").
Enigmatic IBM EPROMs
They came with no further identification, and no hints about their origins, or what machines they may have come from. And just to establish that proper setting of suspense and mystery, neither pair could be content- matched against any known IBM firmware.
Much poking and prying commenced. I didn't delve very deeply into the '25/05/90' odd/ even pair, but it seemed to be some sort of PS/2 BIOS: it proved to contain those telltale extra VGA fonts (on which past verbiage abounds), and to share some other bits and pieces with known Model 35 SX/40 SX ROMs. Seeing that, I prodded the Ardent Tool crew, and Major Tom identified it as rev. 2 of the 35-/40-SX firmware - earlier than other known variants. It's now up for download on the System ROMs page.
The more intriguing one for me was the '1981, 1985' duo (yellow labels in the photo). A cursory look in a hex viewer revealed the following:
EPROM 6448246 has the even addresses, 6448238 the odd addresses.
The internal part numbers are 6480442 and 6480441, respectively.
The BIOS date stamp in the standard location (F000:FFF5) is 03/08/85 .
. At F000:330A, there's yet another date stamp - 02/14/85 .
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