Section 3: Process Description and Control 2026/2027 (6pages)

Question 1 1. What is the purpose of the Process Control Block? 2. Describe the three categories of 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 This study source was downloaded by 100000853002805 from CourseHero.com on 09-21-2026 17:13:26 GMT -05:00 https://www.coursehero.com/file/17770358/03-Process-Control/ 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. Question 3 1. What is the Process Image? 2. What two places does a process image reside? Hint: Suspended Process. 3. What are the five generic steps involved with building a new process image? Answer 1. The process image is the region of memory (disk or main memory) containing the instructions / data / stack of the program being executed. Note that in some models the image may contain also contain the Process Control Block. 2. The process image resides in both the system drive and main memory. The image is initially created on the drive and copied into main memory for execution. A suspended process is one which has been removed from main memory but still resides on the disk so that it can later be restored to main memory for further execution. 3. The five generic steps are: a. Allocate space for the new image on the system (swap) drive. b. Assign a unique process ID (PID) to the new process. c. Create the Process Control Block and other data structures needed by the OS to maintain the process’s execution. d. Copy the image from the system drive into main memory. e. Mark the new process Ready and place in the Ready Queue. Question 4 Using Figure 3.6, describe the process states and conditions that cause a process to transition from one state to another i.e. 1) The transition from New to Ready. 2) The transition from Ready to Running. 3), 4), etc. Answer New to Ready: When a new process has been fully installed by the OS i.e. its Process Control Block has been created, its process image has been created, and it is ready to be installed in the ready queue for its turn at execution.