Amhtsa.134
net.misc
utzoo!decvax!ucbvax!mhtsa!steve
Fri Feb  5 10:24:01 1982
Re: Plural for Unix
According to S. J. Phillips of the BTL Legal and Patent Division, "UNIX"
is not a noun, but an adjective that describes Bell System software
distributed under license.  Thus, "UNIX system" is correct, "UNIX operator"
is incorrect; "UNIX editor" is correct, "UNIX environment" is incorrect.

Thus, the plural of "UNIX system" is "UNIX systems."