Operating System (OS)
The advantage of a command processor running only built-in commands is:

the processing is much faster than would other-wise be the case when user defined commands are used
the command set being common across different hardware configurations
None of these
flexibility to the users in running lists of commands by simply collecting them in named batch command files
users can create system programs and run them as commands

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Operating System (OS)
A critical region is

one which is enclosed by a pair of P and V operations on semaphores
a program segment that often causes unexpected system crashes
none is the above
a program segment that has not been proved bug-free
a program segment where shared resources are accessed

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