By Maya Posch
Publication Date: 2026-04-26 11:00:00
As unloved as IBM’s PCjr was, with only a one-year production run, it’s hard to complain about the documentation available for it. This includes the x86 assembly listing for the BIOS, which [dbalsom] recently used this print version to create an ASM project that can be built into a byte-identical copy of the PCjr BIOS.
In order to build the BIOS image, a ZIP file has been made available that contains the requisite assembler and linker tools, all of which can be run in DOS (or DOSBox) using the provided build.bat file. This creates an executable file, which can then be converted into a BIN file using the provided exe2bin.py Python script, or of course, manually.
This image cannot be used as-is, as the PCjr has its BIOS split across two 32 kB ROMs, so splitting them is required if you intend to burn fresh ROMs. Of note is that the BIOS code is still copyrighted by IBM, so do not take this as some kind of open sourcing, unless you wish to test IBM’s legal…
