Definition of LOCK



The HALT command allows the operator to abort any device channel program

Priviledge Class A

The LOCK command is used to prevent a CP necleus or user VM storage page from being paged in or out. It becomes
locked "in" and always available immeatiately. This must be used sparingly as the available pool of pages drops
with each page locked which can lead to a severe shortage if used to causaly.

Reference the detailed IBM manaul page here.