Question 1

Kernel Mode vs User Mode

Accepted Answer

Kernel mode allows unrestricted access to system resources, while user mode is restricted.

Question 2

Kernel Mode vs User Mode Long

Accepted Answer

Kernel mode executes privileged instructions (like modifying the memory map), while user mode runs applications safely without hardware access.

Question 3

System Call

Accepted Answer

A request from a program to the operating system to perform a specific task.

Question 4

System Call Long

Accepted Answer

Interface between user applications and kernel services. Example: read(), write(), fork(). It triggers a trap instruction to enter kernel mode.

Question 5

Process

Accepted Answer

A program in execution.

Question 6

Process Long

Accepted Answer

Has its own address space, stack, and resources. States include ready, running, and blocked. OS uses a process table to track each process.

Question 7

Multiprogramming

Accepted Answer

Running multiple programs on a CPU by time-sharing.

Question 8

Multiprogramming Long

Accepted Answer

Keeps CPU utilization high by switching between jobs when one waits for I/O, allowing overlap of computation and I/O.

Question 9

Process States

Accepted Answer

The stages a process can be in: ready, running, or blocked.

Question 10

Process States Long

Accepted Answer

Transitions: running→blocked (I/O wait), blocked→ready (I/O done), ready→running (CPU assigned). No direct ready→blocked transition.

Question 11

Critical Section

Accepted Answer

A section of code where shared resources are accessed.

Question 12

Critical Section Long

Accepted Answer

Only one process should be in its critical section at a time to avoid race conditions. Managed by semaphores, mutexes, or monitors.

Question 13

Race Condition

Accepted Answer

When two or more processes access shared data simultaneously, leading to unpredictable results.

Question 14

Race Condition Long

Accepted Answer

Occurs without proper synchronization. Example: two processes updating a shared counter. Solutions include semaphores, locks, and atomic operations.

Question 15

Semaphore

Accepted Answer

A synchronization tool that uses counters to control access to shared resources.

Question 16

Semaphore Long

Accepted Answer

Two operations: wait(P) and signal(V). Ensures mutual exclusion and prevents race conditions in concurrent systems.

Question 17

Deadlock

Accepted Answer

A state where processes wait indefinitely for each other's resources.

Question 18

Deadlock Long

Accepted Answer

Occurs when the four Coffman conditions are met: mutual exclusion, hold and wait, no preemption, circular wait.

Question 19

Scheduling Algorithm

Accepted Answer

Method for deciding which process runs next.

Question 20

Scheduling Algorithm Long

Accepted Answer

Examples: FCFS, SJF, Round Robin, Priority, Multilevel Queue. Criteria: CPU utilization, throughput, turnaround time, waiting time, and response time.

Question 21

Round Robin Scheduling

Accepted Answer

Each process gets CPU time in a cyclic order.

Question 22

Round Robin Scheduling Long

Accepted Answer

Preemptive scheduling with fixed time quantum q. Fair among processes, average turnaround can increase if q is too small or large.

Question 23

Priority Scheduling

Accepted Answer

Processes are executed based on priority.

Question 24

Priority Scheduling Long

Accepted Answer

High-priority processes preempt lower ones. Can lead to starvation; solved by aging (gradual priority increase over time).

Question 25

Average Turnaround Time

Accepted Answer

Average time from process submission to completion.

Question 26

Average Turnaround Time Long

Accepted Answer

mean_turnaround = Σ(finish_time_i) / N. Used to evaluate efficiency of scheduling algorithms.

Question 27

Processor Sharing

Accepted Answer

A system where each process executes one instruction in turn.

Question 28

Processor Sharing Long

Accepted Answer

Simulates fair sharing. If one process takes T seconds alone, n processes take n*T seconds with processor sharing.

Question 29

Real-Time Scheduling

Accepted Answer

Scheduling for tasks with timing constraints.

Question 30

Real-Time Scheduling Long

Accepted Answer

A system is schedulable if Σ(C_i / P_i) <= 1. Example: two voice calls (1ms/5ms) + one video (20ms/40ms) = 0.9, schedulable.

Question 31

Memory Management

Accepted Answer

The process of controlling and coordinating computer memory.

Question 32

Memory Management Long

Accepted Answer

Includes allocation, swapping, paging, and segmentation. OS provides abstraction (virtual memory) and protection between processes.

Question 33

Base and Limit Registers

Accepted Answer

Hardware registers used to define process address boundaries.

Question 34

Base and Limit Registers Long

Accepted Answer

Base stores start address; limit defines range. Logical address + base = physical address. Prevents memory overlap among processes.

Question 35

Virtual Memory

Accepted Answer

A memory abstraction that allows programs to use more memory than physically available.

Question 36

Virtual Memory Long

Accepted Answer

Uses paging or segmentation. Virtual addresses are mapped to physical memory via page tables using an MMU.

Question 37

Paging

Accepted Answer

Dividing virtual memory into fixed-size pages mapped to frames in physical memory.

Question 38

Paging Long

Accepted Answer

Translation uses page tables. Equation: physical_address = frame_number * frame_size + offset.

Question 39

Page Table

Accepted Answer

Data structure that maps virtual pages to physical frames.

Question 40

Page Table Long

Accepted Answer

Stores frame numbers and status bits (valid, dirty, reference). Large tables are optimized with multi-level paging or TLB caching.

Question 41

Translation Lookaside Buffer (TLB)

Accepted Answer

Cache for recent virtual-to-physical address translations.

Question 42

Translation Lookaside Buffer (TLB) Long

Accepted Answer

Speeds up paging by storing recent page mappings. If TLB miss occurs, main memory page table lookup follows.

Question 43

Segmentation

Accepted Answer

Memory division based on logical program units.

Question 44

Segmentation Long

Accepted Answer

Each segment (code, data, stack) has variable size. Logical address = segment number + offset.

Question 45

Page Replacement Algorithm

Accepted Answer

Decides which memory page to remove when a new one is needed.

Question 46

Page Replacement Algorithm Long

Accepted Answer

Examples: Optimal, FIFO, LRU, Second Chance, Clock, Working Set. LRU approximates "recently used" pages using aging algorithms.

Question 47

Working Set

Accepted Answer

The set of pages a process is actively using.

Question 48

Working Set Long

Accepted Answer

Helps control thrashing. Working set size changes dynamically; OS keeps active pages in memory to minimize page faults.

Question 49

Page Fault

Accepted Answer

When a program accesses a page not in physical memory.

Question 50

Page Fault Long

Accepted Answer

Triggers OS to load page from disk. Time cost = disk seek + rotation + transfer.

Question 51

Effective Access Time

Accepted Answer

Average time to access memory considering page faults.

Question 52

Effective Access Time Long

Accepted Answer

EAT = (1 - p) memory_access_time + p page_fault_time, where p = page fault rate.

Question 53

Disk Access Time

Accepted Answer

Time to access data on a disk.

Question 54

Disk Access Time Long

Accepted Answer

T_total = Seek_time + (Rotation_time / 2) + Transfer_time.

Question 55

Bitmap vs Linked List Allocation

Accepted Answer

Methods to track free memory or disk blocks.

Question 56

Bitmap vs Linked List Allocation Long

Accepted Answer

Bitmap uses 1 bit per block; Linked list uses pointers for free regions. Bitmap is compact, linked list is efficient for large free spaces.

Question 57

Inode

Accepted Answer

Data structure storing metadata about a file.

Question 58

Inode Long

Accepted Answer

Contains file size, permissions, timestamps, and block addresses. Inode structure limits maximum file size based on pointer levels.

Question 59

Direct and Indirect Blocks

Accepted Answer

Pointers within an inode that locate file data blocks.

Question 60

Direct and Indirect Blocks Long

Accepted Answer

10 direct + 1 single, double, triple indirect entries. Max file size = B * (D + P + P^2 + P^3), where P = B / pointer_size.

Question 61

File System

Accepted Answer

Component managing files and directories on storage.

Question 62

File System Long

Accepted Answer

Provides abstraction for storage: naming, access, metadata, protection, and persistence across sessions.

Question 63

File System Operations

Accepted Answer

Basic actions to manage files.

Question 64

File System Operations Long

Accepted Answer

Include open, read, write, close, seek, create, delete, and rename. Managed via system calls and directory structures.

Question	Answer
Kernel Mode vs User Mode	Kernel mode allows unrestricted access to system resources, while user mode is restricted.
Kernel Mode vs User Mode Long	Kernel mode executes privileged instructions (like modifying the memory map), while user mode runs applications safely without hardware access.
System Call	A request from a program to the operating system to perform a specific task.
System Call Long	Interface between user applications and kernel services. Example: read(), write(), fork(). It triggers a trap instruction to enter kernel mode.
Process	A program in execution.
Process Long	Has its own address space, stack, and resources. States include ready, running, and blocked. OS uses a process table to track each process.
Multiprogramming	Running multiple programs on a CPU by time-sharing.
Multiprogramming Long	Keeps CPU utilization high by switching between jobs when one waits for I/O, allowing overlap of computation and I/O.
Process States	The stages a process can be in: ready, running, or blocked.
Process States Long	Transitions: running→blocked (I/O wait), blocked→ready (I/O done), ready→running (CPU assigned). No direct ready→blocked transition.
Critical Section	A section of code where shared resources are accessed.
Critical Section Long	Only one process should be in its critical section at a time to avoid race conditions. Managed by semaphores, mutexes, or monitors.
Race Condition	When two or more processes access shared data simultaneously, leading to unpredictable results.
Race Condition Long	Occurs without proper synchronization. Example: two processes updating a shared counter. Solutions include semaphores, locks, and atomic operations.
Semaphore	A synchronization tool that uses counters to control access to shared resources.
Semaphore Long	Two operations: wait(P) and signal(V). Ensures mutual exclusion and prevents race conditions in concurrent systems.
Deadlock	A state where processes wait indefinitely for each other's resources.
Deadlock Long	Occurs when the four Coffman conditions are met: mutual exclusion, hold and wait, no preemption, circular wait.
Scheduling Algorithm	Method for deciding which process runs next.
Scheduling Algorithm Long	Examples: FCFS, SJF, Round Robin, Priority, Multilevel Queue. Criteria: CPU utilization, throughput, turnaround time, waiting time, and response time.
Round Robin Scheduling	Each process gets CPU time in a cyclic order.
Round Robin Scheduling Long	Preemptive scheduling with fixed time quantum q. Fair among processes, average turnaround can increase if q is too small or large.
Priority Scheduling	Processes are executed based on priority.
Priority Scheduling Long	High-priority processes preempt lower ones. Can lead to starvation; solved by aging (gradual priority increase over time).
Average Turnaround Time	Average time from process submission to completion.
Average Turnaround Time Long	mean_turnaround = Σ(finish_time_i) / N. Used to evaluate efficiency of scheduling algorithms.
Processor Sharing	A system where each process executes one instruction in turn.
Processor Sharing Long	Simulates fair sharing. If one process takes T seconds alone, n processes take n*T seconds with processor sharing.
Real-Time Scheduling	Scheduling for tasks with timing constraints.
Real-Time Scheduling Long	A system is schedulable if Σ(C_i / P_i) <= 1. Example: two voice calls (1ms/5ms) + one video (20ms/40ms) = 0.9, schedulable.
Memory Management	The process of controlling and coordinating computer memory.
Memory Management Long	Includes allocation, swapping, paging, and segmentation. OS provides abstraction (virtual memory) and protection between processes.
Base and Limit Registers	Hardware registers used to define process address boundaries.
Base and Limit Registers Long	Base stores start address; limit defines range. Logical address + base = physical address. Prevents memory overlap among processes.
Virtual Memory	A memory abstraction that allows programs to use more memory than physically available.
Virtual Memory Long	Uses paging or segmentation. Virtual addresses are mapped to physical memory via page tables using an MMU.
Paging	Dividing virtual memory into fixed-size pages mapped to frames in physical memory.
Paging Long	Translation uses page tables. Equation: physical_address = frame_number * frame_size + offset.
Page Table	Data structure that maps virtual pages to physical frames.
Page Table Long	Stores frame numbers and status bits (valid, dirty, reference). Large tables are optimized with multi-level paging or TLB caching.
Translation Lookaside Buffer (TLB)	Cache for recent virtual-to-physical address translations.
Translation Lookaside Buffer (TLB) Long	Speeds up paging by storing recent page mappings. If TLB miss occurs, main memory page table lookup follows.
Segmentation	Memory division based on logical program units.
Segmentation Long	Each segment (code, data, stack) has variable size. Logical address = segment number + offset.
Page Replacement Algorithm	Decides which memory page to remove when a new one is needed.
Page Replacement Algorithm Long	Examples: Optimal, FIFO, LRU, Second Chance, Clock, Working Set. LRU approximates "recently used" pages using aging algorithms.
Working Set	The set of pages a process is actively using.
Working Set Long	Helps control thrashing. Working set size changes dynamically; OS keeps active pages in memory to minimize page faults.
Page Fault	When a program accesses a page not in physical memory.
Page Fault Long	Triggers OS to load page from disk. Time cost = disk seek + rotation + transfer.
Effective Access Time	Average time to access memory considering page faults.
Effective Access Time Long	EAT = (1 - p) memory_access_time + p page_fault_time, where p = page fault rate.
Disk Access Time	Time to access data on a disk.
Disk Access Time Long	T_total = Seek_time + (Rotation_time / 2) + Transfer_time.
Bitmap vs Linked List Allocation	Methods to track free memory or disk blocks.
Bitmap vs Linked List Allocation Long	Bitmap uses 1 bit per block; Linked list uses pointers for free regions. Bitmap is compact, linked list is efficient for large free spaces.
Inode	Data structure storing metadata about a file.
Inode Long	Contains file size, permissions, timestamps, and block addresses. Inode structure limits maximum file size based on pointer levels.
Direct and Indirect Blocks	Pointers within an inode that locate file data blocks.
Direct and Indirect Blocks Long	10 direct + 1 single, double, triple indirect entries. Max file size = B * (D + P + P^2 + P^3), where P = B / pointer_size.
File System	Component managing files and directories on storage.
File System Long	Provides abstraction for storage: naming, access, metadata, protection, and persistence across sessions.
File System Operations	Basic actions to manage files.
File System Operations Long	Include open, read, write, close, seek, create, delete, and rename. Managed via system calls and directory structures.
Hard Link vs Symbolic Link	Two ways to reference files.
Hard Link vs Symbolic Link Long	Hard link: same inode, same file. Symbolic link: separate inode pointing by path, can cross filesystems.
File Allocation Methods	How files occupy disk space.
File Allocation Methods Long	Contiguous (fast, fragmentation), Linked (flexible, slow random access), Indexed (direct access via index blocks).
Directory Structure	Organization of files in a hierarchy.
Directory Structure Long	Single-level (flat) or hierarchical (tree). Paths can be absolute (/usr/bin) or relative (../src).
File Attributes	Metadata describing a file
File Attributes Long	Include name, size, type, permissions, timestamps, and owner ID. Stored in inodes or directory entries.
Virtual File System (VFS)	Abstraction layer for file systems.
Virtual File System (VFS) Long	Provides a uniform API to access different file systems (e.g., ext4, FAT32). Uses structures for superblock, inode, and file operations.
Average Memory Access Time (AMAT)	Weighted average access time for cache hierarchy.
Average Memory Access Time (AMAT) Long	AMAT = (Hit_rate_cache T_cache) + (Miss_rate_cache [Hit_rate_RAM T_RAM + Miss_rate_RAM T_disk]).
Page and Offset Calculation	Splitting a virtual address into page and offset.
Page and Offset Calculation Long	VPN = floor(VA / PageSize), Offset = VA mod PageSize.
Schedulability Formula	Condition to check if real-time tasks meet deadlines.
Schedulability Formula Long	Σ(C_i / P_i) <= 1 ensures all tasks are schedulable under EDF.
Turnaround Time Formula	Average time from job submission to completion.
Turnaround Time Formula Long	mean_turnaround = Σ(finish_time_i) / N.
Maximum File Size (Indirect Blocks)	Max file size based on inode pointers.
Maximum File Size (Indirect Blocks) Long	Max_size = B * (D + P + P^2 + P^3), where P = B / a.
Rewind Operation	Moves file read position to start.
Rewind Operation Long	Sequential files use explicit rewind; random-access files use seek(0) to reset the position.
Relative vs Absolute Path	Ways to specify file locations.
Relative vs Absolute Path Long	Absolute starts from root (/home/user); relative is from current directory (../folder).
Linux Command: pwd	Print current working directory.
Linux Command: pwd Long	Displays the full path of the current directory.
Linux Command: ls	List files in directory.
Linux Command: ls Long	Shows directory contents. Options: -l (detailed), -a (include hidden files).
Linux Command: cd	Change directory.
Linux Command: cd Long	Moves into specified directory. Example: cd /usr/local.
Linux Command: mkdir	Create a directory.
Linux Command: mkdir Long	Makes a new directory. Example: mkdir new_folder.
Linux Command: rm	Remove a file.
Linux Command: rm Long	Deletes files; use -r for directories, -f to force removal.
Linux Command: cp	Copy files or directories.
Linux Command: cp Long	Copies files. Example: cp source.txt dest.txt.
Linux Command: mv	Move or rename files
Linux Command: mv Long	Moves or renames. Example: mv old.txt new.txt.
Linux Command: cat	View file contents.
Linux Command: cat Long	Displays file data; can concatenate files.
Linux Command: less	View file contents with navigation.
Linux Command: less Long	Allows scrolling; q to quit.
Linux Command: head	Show first lines of file.
Linux Command: head Long	Displays first 10 lines by default. Example: head -n 20 file.txt.
Linux Command: tail	Show last lines of file.
Linux Command: tail Long	Displays last 10 lines. Option -f follows updates (e.g., logs).
Linux Command: ps	Show running processes.
Linux Command: ps Long	Lists processes owned by current user.
Linux Command: ps aux	Show all processes.
Linux Command: ps aux Long	Displays all processes with details: PID, memory, CPU.
Linux Command: top	Real-time process viewer.
Linux Command: top Long	Displays live CPU/memory usage per process.
Linux Command: chmod	Change file permissions.
Linux Command: chmod Long	Modifies read/write/execute bits. Example: chmod 755 script.sh.
Linux Command: grep	Search text patterns.
Linux Command: grep Long	Finds lines matching regex or text. Example: grep error logfile.txt.
Linux Command: find	Search for files by name.
Linux Command: find Long	Recursively searches directories. Example: find /home -name notes.txt.
Linux Command: ping	Test network connectivity.
Linux Command: ping Long	Sends ICMP echo requests to verify connection.
Linux Command: ssh	Connect to remote system.
Linux Command: ssh Long	Securely logs into another machine. Example: ssh user@host.
Linux Command: scp	Copy files over SSH.
Linux Command: scp Long	Transfers files securely. Example: scp file.txt user@remote:/path/.
Linux Command: df	Show disk usage.
Linux Command: df Long	Reports filesystem space usage. Example: df -h.
Linux Command: free	Show memory usage.
Linux Command: free Long	Displays RAM/swap statistics. Example: free -h.

OS Exam 1

operating systems exam 1

"Know" box contains:
Time elapsed:
Retries: