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] ...
No one who assembles a PC or sets up a new computer can avoid the BIOS or UEFI. That’s where you define the basics, from the boot sequence and memory profiles to security features like Secure Boot.