Operating System
What is Operating System?
A program in execution.
Key formula / rule: Average Waiting Time
Key points
- Understand the concept of a process and its lifecycle.
- Differentiate between process states.
- Explain the role of the Process Control Block (PCB).
- Analyze different CPU scheduling algorithms.
Common exam trap
Confusing processes with programs.
Definitions
- Term
Process
- Meaning
A program in execution.
- Term
Process Control Block (PCB)
- Meaning
A data structure maintained by the operating system for each process, containing information about its state and resources.
- Term
Context Switch
- Meaning
The process of storing the state of a currently running process and restoring the state of another process to allow multitasking.
- Term
Scheduling Algorithm
- Meaning
A method used by the operating system to determine which process in the ready queue should be allocated the CPU next.
- Term
Inter-Process Communication (IPC)
- Meaning
Mechanisms that allow different processes to communicate with each other and synchronize their actions.
- Term
Deadlock
- Meaning
A situation where two or more processes are unable to proceed because each is waiting for the other to release a resource.
Learning objectives
Understand the concept of a process and its lifecycle.
Differentiate between process states.
Explain the role of the Process Control Block (PCB).
Analyze different CPU scheduling algorithms.
Describe context switching and its implications.
Identify mechanisms for Inter-Process Communication (IPC).
Recognize potential issues like deadlocks.
Formulae
- Name
Average Waiting Time
- Note
Crucial for evaluating scheduling algorithms.
- Expression
Sum of waiting × of all processes / Number of processes
- Name
Average Turnaround Time
- Note
Turnaround Time = Completion Time - Arrival Time.
- Expression
Sum of turnaround × of all processes / Number of processes
- Name
Response Time
- Note
Measures interactivity.
- Expression
First Response Time - Arrival Time
Prerequisites
Basic understanding of computer architecture.
Familiarity with memory management concepts.
Knowledge of concurrency and parallelism.
Common mistakes
Confusing processes with programs.
Underestimating the overhead of context switching.
Not considering synchronization issues in concurrent processes.
Incorrectly applying scheduling algorithms.
Ignoring potential deadlock scenarios.
Keywords
Process
Process State
PCB
CPU Scheduling
FCFS
SJN
Round Robin
Priority Scheduling
Context Switch
IPC
Deadlock
Process Synchronization
Practice preview
Consider three processes P1, P2, P3 with arrival times 0, 1, 2 respectively and burst times 5, 3, 2 respectively. Using the Shortest Remaining Time First (SRTF) scheduling algorithm, what is the average waiting time for …
medium
Which of the following is NOT a valid state for a process in an operating system?…
easy
Which of the following CPU scheduling criteria aims to maximize the number of processes completed per unit time?…
easy