5.25in drives did not vanish immediately. The transition occurred over a period of years. What really got things going in PC compatible land was the PS/2 seri

5.25in drives did not vanish immediately. The transition occurred over a period of years. What really got things going in PC compatible land was the PS/2 series of desktops from IBM, which couldn't even fit a 5.25in drive in the case. At around that time it was somewhat common to buy a new PC that had both 5.25in and 3.5in drives, and the common clone makers (Gateway, Packard Bell, et al) could fit either or both in their more-or-less standard PC/AT form factor cases. For a while you could buy software that was on either format, and in some cases, like for utility software (Norton, etc.) they would include both in the box. Back when you still bought software in boxes...