Operating Systems Process Management Quiz

CPU Scheduling

• CPU scheduling selects the next process to run from the ready queue
• A scheduling algorithm determines the selection process
• Scheduling is a fundamental OS function to prevent CPU idleness
• Key aims of scheduling include fairness, efficiency, consistent response time, and minimized response time
• Additional scheduling aims pertain to turnaround time and throughput

Process and Thread Concepts

• A process is a program in execution, sequentially progressing through a defined set of instructions
• Processes require resources like memory, CPU time, and files
• Processes are tracked by the OS using a process table
• Resource allocation occurs upon process creation or during execution
• The OS creates and deletes user and system processes
• Process states transition throughout a program's lifecycle, impacting functionality and execution
• New, ready, running, blocked, and terminated are key process states
•  A process becomes blocked when it waits for an I/O operation to complete or an external event
•  A running process moves to ready state if it reaches its maximum permissible execution time or needs a resource not immediately available.
• A thread is a mini-lightweight process, capable of independent execution separate from other parts of the process. A thread is a basic unit of CPU utilization.
• Creation of a thread/creation of one process from another is called spawning or forking.

Process Control Block (PCB)

• Each process is represented in the OS as a process control block (PCB)
• A PCB maintains information about each process
• This information includes the process's state, program counter, register contents, and other relevant data
• A PCB acts as a repository for process-specific data that may vary across processes

Process Scheduling

• Processes entering a system are put into a job queue
• Each new process is placed in the ready queue
• The selected process enters the running state
• A running process might issue an I/O request, create a sub-process or be forcibly removed.

Concurrent Processes

• Concurrent processes can be independent or cooperating processes
• Independent processes do not interact with other processes
• Cooperating processes interact with each other, potentially affecting one another's operations
• Operating systems allow cooperating processes for sharing information, access to resources, and increased computational speed.

Learning Outcomes

• Students should be able to define processes and threads
• Students should be able to explain and draw process state diagrams, process scheduling diagrams and the PCB
• Students should be able to explain the aims of CPU scheduling
• Students should be able to perform calculations with various scheduling algorithms

Preemptive Scheduling

• Permits temporarily suspending running processes
• Processes relinquish the CPU upon command, allowing higher priority processes to execute
• Includes scheduling algorithms such as round robin, multilevel queue and multilevel feedback queue

Non-preemptive Scheduling

• Processes release the CPU only at completion or voluntary relinquishment
• Scheduling algorithms like first-come, first-served (FCFS), shortest job first (SJF), and priority are examples of non-preemptive approach

Types of Scheduling Algorithms

• Round Robin

• Multilevel Queue

• Multilevel Feedback Queue

• First-in, First-out (FIFO)/First-Come, First-Served (FCFS)

• Shortest Job First (SJF)

• Priority

Calculation Keywords

• CPU utilization
• Throughput
• Turnaround time
• Average turnaround time
• Waiting time
• Average waiting time
• Response time
• Burst time

Quick Review Questions

• Processes in the OS can transition between states
• Some states are impossible; some transition states are dependent on others.
• Processes can have various states based on the OS's design
• In a system with multiple CPUs, a minimum number of processes can exist in ready, running, or blocked states
• System software components like PCBs track and manage these process-related states.

Follow Up Assignment

• Differences among processes and threads are essential components to consider when building and or designing software
• Process state diagrams, and process table diagrams represent essential information