System UICs

As I recall, on VMS, SYSPRV privilege was effectively granted to any
process whose UIC was in a “system” group. By default this was all UICs
from [1,*] to [10,*] (octal), but I recall docs saying the upper limit was
configurable.

I also recall that, when you woke up the login prompt, the LOGINOUT
process was created running under UIC [10,40]. I wonder if this was chosen
to ensure that sysadmins would never lower the upper bound below 10 octal,
they could only raise it? Did the UIC [10,40] have any other significance?
Perhaps something from RSX-11 days?