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:cisin@xenosoft.com]
Sent: Sunday, August 21, 2022 5:40 PM
To: General Discussion: On-Topic and Off-Topic Posts
Cc: t.gardner(a)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.