Processes Chapter Quiz

Process Concept

• A process is an active instance of a program, unlike a program which is passive and stored on disk.
• Key components of a process include the program counter, stack, and data section.
• Process execution follows a sequential order.

Process Memory Structure

• Memory for a process is divided into four sections:
  • Text Section: Contains the compiled program code.
  • Data Section: Holds global and static variables.
  • Heap: Used for dynamic memory allocation.
  • Stack: Stores local variables.

Process States

• Processes change states during execution:
  • New: The process is being created.
  • Ready: The process is ready to execute but waiting for CPU.
  • Running: Instructions are actively being executed.
  • Waiting: The process is waiting for an event or resource.
  • Terminated: The process has finished execution.

Process Control Block (PCB)

• The PCB contains essential information for managing a process, including:
  • Process state and pointer to the parent process.
  • Program counter for the next instruction.
  • Unique process identifier (PID) and CPU registers.
  • Scheduling information including process priority.
  • Memory management and accounting details.
  • I/O status with a list of devices allotted to the process.

Context Switch

• A context switch involves saving the state of the current process and loading the state of a new process.
• The context is represented in the PCB and includes CPU registers and memory management data.
• Context switching incurs overhead and can take between 1 to 1000 microseconds, impacting overall system efficiency.

Process Scheduling

• Process scheduling determines which process in the ready state should move to running.
• Aims for maximal CPU utilization and minimal response time for programs.
• Types of scheduling:
  • Non-pre-emptive: The running process voluntarily yields the CPU.
  • Pre-emptive: The OS interrupts a running process to give CPU to another.

Scheduling Queues

• PCBs are maintained in various scheduling queues:
  • Job Queue: Contains all processes in the system.
  • Ready Queue: Holds processes ready for execution in main memory.
  • Device Queues: Contains blocked processes awaiting I/O device availability.

Schedulers

• Special system software responsible for process scheduling, categorized into:
  • Long-Term Scheduler (Job Scheduler): Controls the admission of processes into the system and manages multiprogramming degree.
  • Short-Term Scheduler (CPU Scheduler): Allocates CPU to ready processes and operates frequently.
  • Medium-Term Scheduler: Manages swapping processes to control the degree of multiprogramming.

Process Creation

• Involves parent processes creating child processes, forming a hierarchical structure.
• Each process is assigned a PID and retains the parent PID for reference.
• Processes can share resources or operate independently based on design.

Fork and Execution

• The fork() system call creates child processes; its return value indicates success or failure.
• Parent processes can either wait for child termination or run concurrently.
• A child process may be a duplicate of its parent or have a new program loaded.

Process Termination

• Processes terminate by executing the last statement and invoking the exit() system call, releasing resources.
• A parent process can abort child processes under specific conditions.
• Processes may also terminate due to system constraints or intervention.
• Orphan and zombie processes arise from improper terminations; orphans are managed by the init system process, while zombies are cleaned up post-parent termination.