OS

Program Counter

A CPU register that holds the memory address of the next instruction to be executed by the processor.

Stack Pointer

A CPU register that points to the top of the current process's stack in memory.

PSW/FLAGS Register

contains critical status information about the processor's current state.

Pseudoparallelism

The illusion that multiple processes execute simultaneously on a single CPU, created by rapid process switching.

Multiprogramming

A technique where multiple programs reside in memory simultaneously, allowing the CPU to switch between them.

Copy-on-Write

An optimization technique where a parent and child process share the same physical memory pages until a write operation occurs.

Context Switch

The process where the CPU stops running one process and saves its state to load another process's saved state.

Critical Region

a segment of code that accesses shared resources and must be executed atomically (as a single, indivisible unit) to prevent data inconsistencies and race condition

Mutual Exclusion

The property that prevents multiple processes from executing critical regions at the same time that access shared resources.

Race Conditions

Situations where the system's behavior depends on the timing of processes, leading to unpredictable results.

Spin Lock

A synchronization mechanism where a process checks a lock variable in a loop until it acquires the lock.

Semaphore

A synchronization primitive that uses a counter to control access to shared resources.

Thread

The smallest unit of execution within a process that can run independently.

Process

The operating system's abstraction of a running program, encompassing its code, data, and execution state.

Kernel

The core component of an operating system with complete control over system resources and operations.

Process Table (proctab) in Xinu

An array where indexes correspond to process IDs, maintaining process state and information.

State Transition

A change in a process's state, governed by specific rules and requiring updates to system data structures.

Quantum

The maximum time a process can run before being preempted to ensure fair CPU scheduling.

Atomic Action

An operation that executes as a single, indivisible unit, ensuring consistency in concurrent systems.

Non-blocking Message Reception

A message reception method that allows a process to return immediately if no messages are available.

Blocking Message Reception

A message reception method where a process waits (blocks) until a message becomes available.

Fork() function

Creates a nearly identical copy of the calling process, resulting in a parent and child process.

Semaphore Wait Operation

Decrements a semaphore's count, potentially blocking the process if resources are not available.

Semaphore Signal Operation

Increments a semaphore's count, potentially waking a waiting process if resources become available.

Ready List

A data structure that contains all processes ready to execute on the CPU.

Sleep Queue Invariant

A process is on the sleep queue if and only if its state is set to blocked with sleep-related status.

Currpid Invariant

A process's PID is stored in this only if its state is set to running.

Race Condition Debugging Difficulty

Race conditions are challenging to debug due to their non-deterministic timing, leading to inconsistent behavior.

Message Passing

A communication method where processes send and receive messages to exchange data.

Priority-based Scheduling

A scheduling method where the highest-priority READY process is selected for execution.

Process Hierarchy

The parent-child relationships between processes, significant for resource management and cleanup.

Preemption

The process of temporarily halting the execution of a currently running process to allow a higher priority process to run.

Why maintain invariants atomically?

To prevent inconsistencies during state transitions, ensuring correctness in process management.