Operating Systems Process and PCB Quiz

Process Concept

• A process is a program in execution.
• A program is a passive entity stored on disk and a process becomes active when loaded into memory.
• One program can be several processes, for example, consider multiple users executing the same program.
• Process execution must progress in sequential fashion.
• A process is composed of the program code, current activity (program counter, processor registers), stack (temporary data), data (global variables), and heap (dynamically allocated memory during run time).

Process State

• A process can transition between different states throughout its execution.
• The possible states are: new (being created), running (instructions being executed), waiting (waiting for some event), ready (waiting to be assigned to a processor), and terminated (finished execution).

Process Control Block (PCB)

• The Process Control Block (PCB) contains information associated with each process.
• PCB is also called the task control block.
• PCB information includes: process state, program counter (location of next instruction to execute), CPU registers, CPU scheduling information (priorities, scheduling queue pointers), memory management information (memory allocated to the process), accounting information (CPU used, clock time elapsed since start, time limits), and I/O status information (I/O devices allocated to process, list of open files).

Process Scheduling

• The process scheduler selects which process should be executed next on the CPU core.
• Goals of process scheduling include maximizing CPU use and quickly switching processes onto the CPU core.
• The process scheduler maintains scheduling queues of processes:
  • Ready queue containing processes residing in main memory and ready to execute
  • Wait queue holding processes waiting for an event (i.e., I/O)
• Processes migrate among the various queues based on their state.

Context Switch

• When the CPU switches to another process, a context switch occurs, saving the state of the old process and loading the saved state for the new process.
• The context of a process is represented in the PCB.
• Context switch is pure overhead, as the system does no useful work during the switch.
• The more complex the OS and the PCB, the longer the context switch.
• Hardware support can influence context switch time. Some hardware provides multiple sets of registers per CPU, allowing multiple contexts to be loaded at once.

Multitasking in Mobile Systems

• Some mobile operating systems (e.g., early iOS versions) restrict execution to one process at a time, while others are suspended.
• The user interface of iOS limits it to a single foreground process controlled by the user and multiple background processes in memory with restrictions.
• iOS background processes are subject to limits including single, short task, receiving notification of events, and specific long-running tasks (e.g., audio playback).
• Android allows foreground and background processes with fewer limitations compared to iOS.
• Background processes in Android can use services to perform tasks.
• A service can keep running even if the background process is suspended and has no user interface with small memory usage.

Test your knowledge on the concepts of processes, their states, and the significance of the Process Control Block (PCB) in operating systems. This quiz will cover key definitions and features of processes in execution, including their transitions and management. Challenge yourself to understand how processes function and are controlled within the OS.