I am getting an old Pentium II going again, intending to install MSDOS 6.22, Windows 95 (on first HD - 545 Mb) and AntiX (on a second HD - 20Gb) in a multi-boot set-up.
I started by partitioning the first HD using cfdisk under a live Slackware CD (Antix would not work - another story), making the first 24Mb for DOS, 200Mb for Win 95, 70 Mb for shared data, and the rest as the Linux Swap. You get the idea - four primary partitons.
Then rebooting with the DOS installation floppy, it asked it it was OK to format the "C:" disk; I accepted and it got on with it. But as soon as it finished, with no by-your-leave, it started formatting the "D:" drive as well - I was not sure if this was the next partion of the first drive (sda2), or the second drive (sdb1). Control-C had no effect (!), so I switched the PC off. Fortunately there was no data on the other partitons.
There seemed to be no way to avoid this arrogant behaviour (I tried it again). I then disconnected the second hard drive (at least to save the time formatting 20Gb), rebooted, and this time it went straight into copying from the floppy onto the now formatted sda1. It never seemed to notice the other partitons on the first drive.
Yet when MSDOS 6.22 came out (1993) there were certainly other OS's around that might have been overwritten on the other drive - OS/2, and MS's own NT.
Unsolved mysteries of the Universe, No 13 :-
How many remakes of Anna Karenina does the World need?