On 18 Feb 2020 15:04 -0800, from bakul at bitblocks.com (Bakul Shah):
> IIRC even the original IBM PC came with schematics.

I'm not completely sure about the schematics, but the full, commented,
BIOS source code listing definitely was available in IBM's own
Technical Reference.

http://www.bitsavers.org/pdf/ibm/pc/pc/6025008_PC_Technical_Reference_Aug81.pdf
(the BIOS source code listing begins at page 192 of the PDF).

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