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OS midterm

QuestionAnswer
Operating System The software layer that manages hardware resources and provides services for application programs.
Memory Manager Allocates RAM
Processor Manager Assigns CPU time
Device Manager Controls I/O devices
File Manager Organizes files
Allocation Assign resources to processes.
Monitoring Track usage and performance.
Protection Prevent unauthorized access.
Deallocation Free resources when done.
Main Memory (RAM) Volatile storage for active processes.
Register Fast
CPU Executes instructions.
Bit/Byte/KB Units of digital data (1 byte = 8 bits).
System Software OS
Application Software Programs like browsers
Batch Processing Jobs queued and run without user interaction.
Interactive User inputs affect processing in real time.
Real-Time Immediate response required (e.g.
Multiprogramming OS switches between jobs actively.
Passive Multiprogramming Jobs wait for I/O; CPU idle during wait.
Single-user system One job in memory at a time.
Fixed Partitions Memory divided into fixed sizes; leads to internal fragmentation.
Dynamic Partitions Memory allocated as needed; can cause external fragmentation.
Relocatable Dynamic Partitions Jobs can be moved to reduce fragmentation.
Compaction Rearranges memory to consolidate free space.
Relocation Register Used to adjust logical addresses to physical addresses when jobs are moved.
First-Fit Allocates first block large enough.
Best-Fit Allocates smallest block that fits.
Fragmentation Wasted space inside allocated block.
Internal Fragmentation Wasted space inside allocated block.
External Fragmentation Wasted space between blocks.
Throughput Measure of how many jobs complete per time unit.
Page Fixed-size block of logical memory.
Frame Fixed-size block of physical memory.
Paged Allocation Breaks jobs into pages
Demand Paging Loads pages only when needed
Job Table (JT) Tracks job size and location.
Page Map Table (PMT) Maps logical pages to physical frames.
Memory Map Table (MMT) Tracks frame usage.
Address Calculation 1. Identify page number. 2. Find frame number from PMT. 3. Add offset to frame base. 4. Get physical address.
Page Fault Occurs when a page is not in memory.
Page Replacement Policies FIFO
Thrashing Excessive page faults causing low performance.
Belady's Anomaly FIFO can perform worse with more frames—counterintuitive!
Working Set Set of pages actively used by a process.
Virtual Memory Allows programs to use more memory than physically available via paging.
Single Processor One CPU.
Multiprocessor Multiple CPUs sharing memory.
Clustered Systems Networked computers working together.
Processor Hardware executing instructions.
Process Program in execution.
Job Scheduler Selects jobs to load.
Process Scheduler Selects process to run next.
I/O-Bound Spends more time on I/O.
CPU-Bound Spends more time on computation.
Process States New
Process Control Block (PCB) Stores process info: ID
Context Switching Saving and restoring process state during CPU switch.
FCFS First job runs first.
SJN Shortest job runs first.
SRT Job with least remaining time runs.
Round Robin Each job gets equal time slice.
Time Slice / Quantum Fixed time a process runs before switching.
Response Time Time from request to first response.
Gantt Charts Visual timeline of process execution.
Turnaround Time Completion Time - Arrival Time.
Wait Time Turnaround Time - Burst Time.
Cache Memory Fast memory between CPU and RAM; stores frequently used data.
Created by: user-1877945
 



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