On 03/05/2014 16:25, John Williamson wrote:
One reason for making it the size it is could have been that they may
have looked forwards (As engineers often do) and foreseen that the CD
drive could replace the 5 1/4" floppy drive in a standard computer case.

I have long assumed that all disc sizes were derived from standard rack
mounts. (With the odd exception such as the 3" drive used in some
Amstrad machines.) So I'd go along with that but maybe as a pre-recorded
CD-ROM rather than a rewritable device like a floppy?

'Tis a pity they didn't adopt a standard screw for fixing all drives...

--
Rod