2 cissp ® Official Study Guide Eighth Edition

Process States
Also known as 
operating states
, 
process states
are various forms of execu-
tion in which a process may run. Where the operating system is concerned, it can be in 
one of two modes at any given moment: operating in a privileged, all-access mode known 
as 
supervisor state
or operating in what’s called the 
problem state
associated with user 
mode, where privileges are low and all access requests must be checked against credentials 
for authorization before they are granted or denied. The latter is called the problem state 
not because problems are guaranteed to occur but because the unprivileged nature of user 
access means that problems can occur and the system must take appropriate measures to 
protect security, integrity, and confidentiality.
Processes line up for execution in an operating system in a processing queue, where they 
will be scheduled to run as a processor becomes available. Because many operating systems 
allow processes to consume processor time only in fixed increments or chunks, when a new 
process is created, it enters the processing queue for the first time; should a process con-
sume its entire chunk of processing time (called a 
time slice
) without completing, it returns 
to the processing queue for another time slice the next time its turn comes around. Also, 
the process scheduler usually selects the highest-priority process for execution, so reaching 
the front of the line doesn’t always guarantee access to the CPU (because a process may be 
preempted at the last instant by another process with higher priority).
According to whether a process is running, it can operate in one of several states:
Ready
In the 
ready state
, a process is ready to resume or begin processing as soon as it is 
scheduled for execution. If the CPU is available when the process reaches this state, it will 
transition directly into the running state; otherwise, it sits in the ready state until its turn 
comes up. This means the process has all the memory and other resources it needs to begin 
executing immediately.