COM S 352 Operating Systems Exam Acronyms and Reference

Vocabulary practice flashcards covering operating systems midterm acronyms, general concepts, processes, CPU scheduling algorithms, memory translation, and page replacement policies.

OS (Operating System)

Manages hardware resources, protects processes, and provides services to programs. Memory cue: Manager of a shared workshop.

CPU (Central Processing Unit)

Executes program instructions. Memory cue: The worker carrying out the instructions.

I/O (Input/Output)

Communication with devices, such as disks, keyboards, and displays. Memory cue: Deliveries arriving at or leaving the workshop.

PID (Process Identifier)

An ID number identifying a process. A successful exec() keeps the same PID. Memory cue: A worker's employee ID.

PCB (Process Control Block)

The OS record used to manage a process, including its state, saved execution context, and memory-management information. Memory cue: A worker's record folder and progress notes.

API (Application Programming Interface)

An interface software uses to access functions or services. An API call is not necessarily a system call. Memory cue: A service menu explaining what you can request.

RAM (Random Access Memory)

Working memory holding instructions and data in use. Ordinary RAM is volatile: its contents are lost without power. Memory cue: The desk holding work currently in progress.

FIFO (Scheduling)

First In, First Out: Run ready jobs in arrival order. Standard FIFO scheduling is nonpreemptive. Memory cue: First in line goes first.

SJF (Shortest Job First)

Choose the ready job with the shortest next CPU burst. In the nonpreemptive version, the running burst is not interrupted by a shorter arrival. Memory cue: Serve the shortest transaction next, but finish the current customer.

STCF (Shortest Time to Completion First)

Run the job with the least remaining CPU time. A shorter arriving job can preempt the current job. Memory cue: Pause a long transaction to serve a shorter one.

RR (Round Robin)

Give ready processes repeated turns of up to one time quantum. A process can finish or block before its quantum expires. Memory cue: Take turns around a circle.

MLFQ (Multilevel Feedback Queue)

Use multiple priority queues and adjust priority based on behavior. Consuming a level's CPU allotment generally leads to demotion; periodic priority boosts help prevent starvation. Memory cue: Quick questions get prompt help; lengthy tasks move to longer work sessions.

CFS (Completely Fair Scheduler)

Share CPU time according to process weights and virtual runtime. Generally choose the runnable process with the smallest virtual runtime. Lower nice values receive a larger CPU share, not guaranteed first service. Memory cue: Track weighted service received and help the person with the lowest tally.

Lottery

A scheduling policy that chooses a winning ticket randomly.

Stride

A scheduling policy that chooses the lowest pass value, then adds that process's stride.

MMU (Memory Management Unit)

Hardware that translates virtual addresses and enforces memory-access protection using information configured by the OS. Memory cue: A security gate following rules written by the OS.

VPN (Virtual Page Number)

Identifies a page within a process's virtual address space. Memory cue: Which page in your personal book?

PFN (Physical Frame Number)

Identifies a fixed-size frame in physical memory. Translation replaces the VPN with the PFN and keeps the offset. Memory cue: Which physical drawer holds that page?

PTE (Page Table Entry)

One page-table record containing mapping and status/protection information for a virtual page. Memory cue: One row in the page-to-drawer directory.

PDE (Page Directory Entry)

In a two-level page table, an entry used to locate a lower-level page table. Unused regions need not have lower-level tables allocated. Memory cue: An index pointing to a smaller directory.

TLB (Translation Lookaside Buffer)

A fast cache of recent virtual-page-to-physical-frame translations. A TLB miss does not necessarily mean a page fault or disk access. Memory cue: A sticky note with a frequently used directory lookup.

FIFO (Page Replacement)

First In, First Out: Evict the page loaded earliest. Accessing it again does not reset its place in FIFO order. FIFO can experience Belady's anomaly. Memory cue: The book that arrived on the desk first leaves first.

LRU (Least Recently Used)

Evict the page whose most recent access was longest ago. A new access updates its recency. LRU does not experience Belady's anomaly. Memory cue: Remove the book you have gone longest without opening.

OPT (Optimal Page Replacement)

Evict the page whose next access is farthest in the future. A page never accessed again is an ideal victim. Requires knowledge of future accesses. Memory cue: Use your future reading schedule to decide which book to remove.