pcjs/devices/pcx86/rom/compaq/portable

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Compaq Portable Computer ROMs

The oldest COMPAQ Portable Computer ROM I have is an 8Kb Rev C ROM from a REV D system board.

Printed on the back of the system board:

(C) COMPAQ COMPUTER CORP. 1982
BOARD NO. 000006-001   REV D 84490

Curiously, the system board contains two mask ROMs (AM9265DPC), both labeled 1000666-001 REV.C but with two different identifiers: 34569 8350KME on the ROM in socket U40, and 34569 8350LME on the ROM the socket below U40. However, when I dumped the ROMs with my homemade ROM reader, their contents were identical.

I've seen pictures of other COMPAQ Portable system boards with only one mask ROM installed, so I'm puzzled as to why my board contains two. Do the contents of the second ROM show up in a different part of the address space? Unless I'm someday able to power and test this board, I may never know.

Some clues can be found in this COMPAQ Portable/Plus Maintenance Guide (Excerpt). Older (REV B) system boards apparently did require 2 ROMs, at locations U40 and U47. REV C and later system boards required only 1 (REV C or later) ROM at location U40.

That's all well and good, but it still doesn't explain why my REV D system board contains 2 ROMs. It just raises more questions. For example, why did older system boards require 2 ROMs? Were the earlier BIOS revisions larger or the ROMs smaller (eg, 4Kb instead of 8Kb)?

Also, I've come across some other computer history sites that claim the COMPAQ Portable contained "12Kb" of ROM. Hmmm.

System ROM Revisions

Thanks to the aforementioned Maintenance Guide excerpt, we know that these other COMPAQ Portable ROM revisions existed; however, REV C is the only revision currently available here.

Rev  ROM #       Size  Date
---  ----------  ----  ----
B    100518-001
C    100666-001   8Kb  None
E    100298-004
F    100298-005
G    105681-001
H    106265-001
J    106265-002