For anyone interested in the history of UNIX on PCs, an article rather appropriately called UNIX Packages For The PC on page 40 of the Nov-Dec 1989 issue (#50) of Micro Cornucopia ought to be interesting. Now available in PDF on bitsavers.org.
The first part of the article covers the general situation of UNIX on PCs and explains the various ports of AT&T’s code to the PC platform (XENIX, microports/Microport, ISC…). The general structure of UNIX (base OS, development, text processing, documentation, etc.) is also explained.
The second part briefly covers several PC UNIX implementations: SCO XENIX (not SCO UNIX just yet), ISC 386/ix, Everex ESIX, Dell UNIX, and one variant that does not ring any bells—Bell UNIX, which apparently had just been acquired by Intel. Perhaps that is the same product which was later sold as AT&T UNIX… or perhaps not?