Sorry, there was no U consideration in the FH 5¼-inch form factor decision. It is 5.75 in × 3.25 in × 8 in; none of these have integer "U" relationships.
SA engineering studied the various 8-track tape drives then available and found no standard form factor so they picked a set of numbers that they thought would work for most and for the Wang application in particular. No one mentioned U dimensions as a consideration. I seem to recall most 8-track tape drives were mounted horizontally which would make the U height 3.5-inches not 3.25 inches. -----Original Message----- From: Fred Cisin [mailto:ci...@xenosoft.com] Sent: Sunday, August 21, 2022 5:40 PM To: General Discussion: On-Topic and Off-Topic Posts Cc: t.gard...@computer.org; Tom Gardner Subject: RE: [cctalk] Re: Wang bar napkin story [WAS:RE: Re: "Revival" of a dedicated Micropolis webpage on internet] On Mon, 22 Aug 2022, W2HX wrote: > I always thought it was interesting how 5 1/4 is 3U (rack units). I > thought there might have been some relationship to that. But could > have been just coincidence. I think that it is related. I think that the drive (not the diskette) was apparently intended to be mountable where certain tape drives were mounted.
