Section 3: Process Description and Control
Question 1
1. What is the purpose of the Process Control Block?
2. Describe the three categories of
... [Show More] information present in the process control
block as shown in Figure 3.13 in the text book.
3. What is being represented in Figure 3.14?
Answer
1. The process control block contains the information needed by the
operating system to maintain and schedule the process.
2. A) Process Identification Information contains information that identified
the process. For example the PID, PPID, UID, and GID.
B) Processor State Information contains information (PC, SP, registers,
etc.) that describes the processor state when the processor was last
interrupted and is needed to restore the process back into a running state.
C) Process Control Information contains the information used by the OS to
schedule and manage the execution of individual processes. For example,
process state, priority, owned resources (file & socket descriptors),
accounting information (CPU & wall clock times).
3. Figure 3.14 describes how the operating system maintains a number of
queues and collections that reference lists of PCB. In the figure, an
operating system data structure maintains references to processes that
are in the Running, Ready, or Blocked state.
Question 2
1. Explain the meaning of a process’s instruction trace.
2. Explain the instruction trace presented in Figure 3.4 in the book. What is
meant by Time-Out and by I/O Request?
3. Explain the role of the dispatcher service in all of this. How is the
dispatcher represented in Figure 3.4?
Answer
1. The instruction trace is a list (or trace) of the instruction address that a
process executes over some given time range.
2. Figure 3.4 illustrates the execution of three processes interleaved with the
dispatcher’s execution. The execution of a process divided into slices and
every eligible process is to be given a turn executing. The process’s
execution can be interrupted for two reasons in this example. Either the
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process executes a Blocking I/O Request (Blocking SYSCALL) or it
executes for the full duration of its time-slice and is preempted by time-out
interrupt.
3. The dispatcher is the OS mechanism that selects, installs, and allows to
execute a “ready to execute” process from the Read Process Queue. The
dispatcher’s execution is represented by the blue shaded traces which
execute the same instructions each time. [Show Less]