This takes me way back... Compaq business computers in the 90s were not very nice to set up, although they worked ok.
You could get 100, 120, 133, 166MMX, 200, 233, 266, 300 and 333MHz models (this was an era of rapid hardware development - you got whatever was the latest at the time).
The BIOS, as you've discovered, lived on a partition and came supplied on the hard drive. But, it could get deleted or corrupted, or you might upgrade the drive. So you'd have to reinstall it from floppies.
Once done, then you would normally install DOS with Windows 3.1, or Windows for Workgroups 3.11. I suppose you could install Windows 95, if the drivers could be found.
After this series, they moved on to the 350, 400, 450 and 500 MHz models which had the bios inbuilt in the conventional manner. These were exceptionally well-engineered, and can be expected to still work today.