[PhantomGremlin]

the machine would be bootable with the defaults

The good-old-days weren't all Wine and Roses. For example, there was this: http://webpages.charter.net/danrollins/techhelp/0054.HTM

If you wiped out CMOS, a "simple CMOS reset" was not sufficient to allow booting, because knowledge of the type of disk you had installed was lost.

Sure, you could iterate thru those preloaded disk types and stumble upon the correct one. BUT, having a fixed selection of types proved to be too limiting. So there was a scheme to add drives types. That info was also stored in CMOS, so if you lost that, it was quite difficult to restore the configuration:

   Newer BIOSes provide a means to define a custom
   setting.  The setting will be stored in an
   undocumented location in CMOS memory (and is lost
   if the battery ever fails -- so write it down!)

It wasn't an insurmountable problem. It simply meant that you had to come up with a few bytes, perhaps by calling the manufacturer or integrator. But this was in the days before Google, so it wasn't easy to find this info with a quick search.

[userbinator]

Drives have had CHS values printed on them since the very beginning. It does mean you have to open the case to read it, but you do have to open the case to reset CMOS anyway...

But the problem of drive geometry detection essentially disappeared with IDE autodetection, which quickly became the norm sometime in the early 90s.