> IBM released the PC with ... source code for the BIOS.
Um, no they didn't. The BIOS was very much a blob. Compaq spent a significant amount of resources reverse-engineering the BIOS, which made the IBM-PC-compatible market possible.
You're right that Compaq went to a lot of reverse engineering effort, userbinator is also right about IBM releasing the source code for their BIOS. They did it to prevent reverse engineering by tainting anyone exposed to the code. https://en.m.wikipedia.org/wiki/Phoenix_Technologies
