I dunno, BIOS was pretty opaque and all the major BIOS vendors stuff was completely proprietary (and often full of bugs). The difference is that BIOS was simpler and hence easier to understand. It was also not as well-protected and if you wanted to you could extract and reverse engineer the BIOS with easily available tools. Nowadays the firmware in your machine is better protected as well as much more complex, making it harder to access and harder to understand.