Processes, Scheduling, IPC & Threads – Vocabulary Flashcards

These vocabulary flashcards cover fundamental terms related to processes, scheduling, interprocess communication, and threads, providing concise definitions for exam review.

Process

A program in execution, including current register values, program counter, and memory sections.

Program

A passive entity stored on disk (executable file) that becomes a process when loaded into memory.

Multiprogramming

Rapid CPU switching among processes to keep the CPU busy and maximize utilization.

Batch System

Operating-system environment that executes jobs with minimal user interaction.

Time-Shared System

Environment that rapidly switches the CPU among user programs (tasks) to give interactive response.

Text Section

The portion of a process containing executable program code.

Process Stack

Area in a process memory holding temporary data such as parameters, return addresses, and local variables.

Data Section

Part of a process memory that stores global variables.

Heap

Memory region in a process for dynamically allocated data at run time.

Process State – New

State in which a process is being created.

Process State – Running

State where CPU instructions of the process are actively executing.

Process State – Waiting

State where a process waits for an event (e.g., I/O completion).

Process State – Ready

State where a process is prepared to run and awaiting CPU allocation.

Process State – Terminated

State reached after a process finishes execution.

Process Control Block (PCB)

Data structure used by the OS to store all information about a particular process.

Program Counter (in PCB)

Field indicating the address of the next instruction for the process.

CPU-Scheduling Information

Part of PCB holding priority, queue pointers, and other scheduling parameters.

Memory-Management Information

PCB fields containing base/limit registers, page or segment tables.

Accounting Information

PCB data such as CPU time used, job numbers, and time limits.

I/O Status Information

PCB list of allocated devices and open files for the process.

Context Switch

Saving the state of one process and restoring another so the CPU can switch execution.

Ready Queue

Linked list of PCBs for processes in main memory waiting to run.

Job Queue

Collection of all processes in the system.

Device Queue

Queue of processes waiting for a particular I/O device.

Long-Term Scheduler (Job Scheduler)

OS component that selects which jobs are loaded into memory.

Short-Term Scheduler (CPU Scheduler)

Component that chooses which ready process gets the CPU next.

Medium-Term Scheduler

Scheduler that swaps processes in and out of memory to improve the mix; supports swapping.

CPU-Bound Process

Process spending most of its time doing computations and making few I/O requests.

I/O-Bound Process

Process that spends more time on I/O than CPU computation.

Swapping

Removing a process from memory and later reloading it to continue execution.

Parent Process

A process that creates one or more child processes.

Child Process

Process created by another process (its parent).

Process Identifier (PID)

Unique integer assigned to each process for indexing its attributes.

Process Tree

Hierarchical representation showing parent-child relationships among processes.

Orphan Process

Child whose parent has terminated; re-parented to init in UNIX/Linux.

Zombie Process

Terminated process whose parent has not yet called wait(); its PCB entry remains for exit status.

Cascading Termination

OS-initiated termination of all child processes if a parent exits in systems that disallow independent children.

Interprocess Communication (IPC)

Mechanisms permitting processes to exchange data and synchronize.

Independent Process

Process that cannot affect or be affected by others and shares no data.

Cooperating Process

Process that can affect or be affected by others via shared data or communication.

Shared-Memory Model

IPC model where cooperating processes communicate by reading/writing a common memory region.

Message-Passing Model

IPC model where processes exchange data via send() and receive() operations.

Producer–Consumer Problem

Classic shared-memory synchronization scenario where producers generate data consumed by consumers.

Bounded Buffer

Fixed-size circular buffer used in producer-consumer problem; full/empty conditions require waiting.

Unbounded Buffer

Logical buffer with no capacity limit; producer never waits for space.

Mailbox (Port)

Named object for indirect message passing where multiple processes can deposit and remove messages.

Blocking Send

Send operation that suspends the sender until the message is received.

Nonblocking Send

Send operation that returns immediately after queuing the message.

Blocking Receive

Receive operation that blocks until a message is available.

Nonblocking Receive

Receive that returns immediately with a message or null if none available.

Zero-Capacity Link

Message queue of length zero; sender blocks until receiver accepts the message.

Bounded-Capacity Link

Message queue with finite length n; sender blocks only when the queue is full.

Unbounded-Capacity Link

Message queue with infinite length; sender never blocks.

Scheduler

OS module that makes decisions about which process or thread runs next.

Dispatcher

Module that performs context switch, mode switch, and jumps to selected process code.

Preemptive Scheduling

Scheduling where the OS can take the CPU away from a running process.

Non-Preemptive Scheduling

Scheduling where a running process keeps the CPU until it blocks or terminates.

CPU Burst

Period during which a process runs on the CPU before doing I/O.

I/O Burst

Time interval where a process waits for I/O after a CPU burst.

Scheduling Criteria – CPU Utilization

Percentage of time the CPU is busy; higher is better.

Scheduling Criteria – Throughput

Number of processes completed per time unit.

Scheduling Criteria – Turnaround Time

Total time from process submission to completion.

Scheduling Criteria – Waiting Time

Total time a process spends in the ready queue.

Scheduling Criteria – Response Time

Time from request submission to first response output.

Fairness

Degree to which each process gets an equitable share of CPU time.

FCFS Scheduling

First-Come, First-Served algorithm that runs jobs in arrival order; non-preemptive.

Convoy Effect

Situation in FCFS where one long CPU-bound job delays many I/O-bound jobs.

Shortest Job First (SJF)

Algorithm that selects the process with the shortest CPU burst; optimal for avg waiting time.

Shortest Remaining Time First (SRTF)

Preemptive version of SJF that always runs the job with the smallest remaining burst.

Priority Scheduling

Algorithm that allocates CPU to highest-priority process; can be preemptive or non-preemptive.

Starvation

Indefinite blocking of low-priority processes in priority scheduling.

Aging

Technique of gradually increasing waiting processes’ priorities to prevent starvation.

Round Robin (RR)

Preemptive algorithm using time quantum q and cyclic order through ready queue.

Time Quantum (Time Slice)

Fixed CPU time a process can run before being preempted in RR scheduling.

Thread

Lightweight unit of CPU utilization within a process, having its own PC, registers, and stack but sharing code and data.

Multithreaded Process

Single process containing multiple threads that share resources but execute concurrently.

Advantages of Threads

Lower context-switch overhead, easier communication, improved concurrency, and better multiprocessor utilization.