14" drives - full rack width, with room for some casting on either side. 8" drives - two side-by-side in a rack width. (Perfect fit, in fact.) 5.25" drives - probably completely unconstrained by rack widths. I think a recent document on bitsavers details the IBM DemiDiskette, which was something like 4" :-). Height of a FH 5.25" drive is the same as an 8" drive. 3.5" drives - ???? No idea There was a joke in BYTE in the early 80's about diskette manufacturers keeping the punched out "holes" from each size of floppy for use as future floppy sizes :-). Tim.