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    Processes, Threads, System Calls and Context Switching Practice Questions for GATE CS

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    Processes, Threads, System Calls and Context Switching Practice Questions for GATE CS

    Solve 0+ Processes, Threads, System Calls and Context Switching practice questions for GATE CS with answers and detailed solutions. Free sample questions below.

    Chapter Roadmap: Processes, Threads, System Calls and Context Switching

    Chapter Journey: 4 Topics, One Clear Path

    This chapter builds your understanding of how the operating system manages execution. Here is what you will master:

    Topic 1: Process States, Ready Queues and Context Switching (Current)
    • Understand the lifecycle of a process: new, ready, running, blocked, terminated
    • Learn how the OS maintains ready queues and decides which process runs next
    • Master context switching: what gets saved, what gets loaded, and the overhead involved
    • Foundation for everything else in this chapter
    Topic 2: Threads and Thread Context
    • Threads as lightweight units of execution within a process
    • What threads share versus what they keep private
    • Thread context switching versus process context switching
    Topic 3: System Calls and User-Kernel Mode Transitions
    • The boundary between user mode and kernel mode
    • How programs request OS services through system calls
    • The mechanism of mode transition and its triggers
    Topic 4: Process Creation using Fork and Wait
    • The fork system call: creating child processes
    • Understanding parent-child relationships
    • The wait system call: synchronization between processes
    What You Will Achieve:

    By the end of this chapter, you will be able to trace process state transitions, calculate context switch overhead, distinguish between process and thread behavior, predict the number of processes created by fork loops, and identify which operations trigger user-to-kernel mode transitions.

    What is a Process? The Unit of Execution

    Process = Program in Execution

    A process is a program in execution. It is the fundamental unit of work in a modern operating system.

    Program versus Process

    AspectProgramProcess
    NaturePassive entityActive entity
    StorageStored on diskLoaded in memory
    AnalogyRecipe in a cookbookThe act of cooking
    LifetimePermanent fileTemporary execution

    What Makes Up a Process?

    A process in memory contains:

    1. Text section: The compiled program code
    2. Program counter: Points to the next instruction to execute
    3. Stack: Temporary data, function parameters, return addresses, local variables
    4. Data section: Global variables
    5. Heap: Dynamically allocated memory (grows during execution)

    Process Control Block (PCB)

    The operating system tracks each process using a Process Control Block (PCB). Think of it as the process identity card. It contains:

    • Process state: current state (new, ready, running, blocked, terminated)
    • Program counter: address of next instruction
    • CPU registers: contents of all registers when process was last running
    • CPU scheduling information: priority, pointers to scheduling queues
    • Memory management information: base and limit registers, page tables
    • Accounting information: CPU time used, time limits, process number
    • I/O status information: list of I/O devices allocated, open files

    The PCB is the key data structure that allows the operating system to support multiple processes simultaneously.

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