[TUHS] SVR4 vs. Solaris 2

[segaloco via TUHS]

Pardon if this question has already been asked and answered
before, but I find myself curious.  System V Release 4 was a
joint effort between USL and Sun, which involved contributions
from both parties as well as other improvements.

I often see it suggested that the first version of Solaris was
SVR4 itself, but my question is: Was the initial stock Solaris 2
release identical to USL SVR4, or were there still additional
value-adds that Sun made to the inaugural release of Solaris
beyond just the joint SVR4 trunk resulting from the project
between the two organizations?  In other words, when one
purchased and installed the initial release of Solaris, were they
in essence also installing SVR4 from USL, or was there some
appreciable difference?

- Matt G.