Patent on UNIX set-UID

[Kevin P. Kleinfelter]

I frequently read that UNIX's set-UID bit was one of the first software
patents.  What protection is claimed/provided under this patent?
Operating systems such as MINIX (functionally equivalent to SYS 7, but
not containing ONE line of actual AT&T code) provide the set-UID feature.
Are they violating the patent?  Should someone (Prentice-Hall in the
case of MINIX) be paying a patent fee for distributing the operating system
which uses this patented concept?  If not, why not?
-- 
Kevin Kleinfelter @ Management Science America, Inc (404) 239-2347
gatech!nanovx!msa3b!kevin