Computer Notes | JKSSB / JKPSC / FAA / Junior Assistant
Operating System — Complete JKSSB Notes
All PYQs, Concepts & New Pattern MCQs
Types of OS · Windows/Linux/DOS · File Systems · Scheduling · Memory Management · 40+ PYQs
📌 Why This Topic Matters for JKSSB
Operating System questions appear in every single JKSSB Computer Awareness section — Junior Assistant, FAA, Panchayat Secretary, Wildlife Inspector, Accounts Assistant, Graduate Level. Expect 4–8 questions per paper from OS alone. This post covers every concept, every Windows version, all OS types, file systems, scheduling, and all known PYQs with full explanations.
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1. What is an Operating System?
An Operating System (OS) is system software that acts as an intermediary between the user and computer hardware. It manages all hardware and software resources of a computer and provides a platform for other programs to run.
Developed by: The concept of OS was pioneered through UNIX (1969, Bell Labs — Ken Thompson & Dennis Ritchie). The first widely used PC OS was MS-DOS (1981, Microsoft).
Functions of an Operating System
🖥️ Process Management
Creates, schedules and terminates processes. Allocates CPU time to each process. Handles multitasking.
💾 Memory Management
Allocates and deallocates RAM to programs. Manages virtual memory, paging, and segmentation.
📁 File Management
Creates, deletes, reads, writes files. Organises files in directories. Manages file permissions and access control.
⚙️ Device Management
Controls hardware devices via device drivers. Manages I/O operations between CPU and peripherals.
🔐 Security & Protection
Controls user access, authentication, file permissions. Protects data from unauthorised access.
🖱️ User Interface
Provides CLI (Command Line Interface) or GUI (Graphical User Interface) for user interaction with the system.
CLI vs GUI — Most Asked Comparison
| Interface Type | Description | Examples |
|---|---|---|
| CLI (Command Line Interface) | Text-based. User types commands. Fast, efficient for experts. Uses less memory. E.g., MS-DOS, Linux Terminal, Command Prompt | MS-DOS, Linux/Unix Shell, Windows Command Prompt |
| GUI (Graphical User Interface) | Uses visual elements — icons, windows, menus, mouse clicks. User-friendly. Uses more memory. E.g., Windows, macOS | Windows, macOS, Android, Ubuntu Desktop |
2. Types of Operating System
| Type | Key Feature | Examples | Exam Status |
|---|---|---|---|
| Batch OS | Jobs are grouped into batches and processed sequentially without user interaction. No direct user-computer interaction. | Old IBM mainframes, early computers. Punch card era. | JKSSB PYQ ⭐ |
| Time-Sharing OS (Multitasking) | Multiple users share CPU time simultaneously. CPU switches between tasks very rapidly giving illusion of parallel execution. Also called Multitasking OS. | UNIX, Linux, Windows — modern OS all use time-sharing | Most Asked ⭐⭐ |
| Real-Time OS (RTOS) | Processes data in real time — within a guaranteed time constraint. Two types: Hard RTOS (strict deadlines — life-critical) and Soft RTOS (best effort). | Hard: Aircraft systems, pacemakers, nuclear reactors. Soft: Multimedia streaming, online transactions | Important PYQ |
| Distributed OS | Multiple computers networked together appear as a single unified system to users. Resources shared across network. | Google's server infrastructure, cloud computing systems | Asked in Graduate Level |
| Embedded OS | Designed for embedded systems — devices with specific, limited functions. Very small memory footprint. | ATM machines, washing machines, microwave ovens, printers | Asked in FAA |
| Multi-User OS | Allows multiple users to access the computer simultaneously — either through terminals or network. | UNIX, Linux servers, Windows Server | Common PYQ |
| Single-User OS | Only one user can work at a time. Simple design. | MS-DOS, early Windows (3.1) | Basic concept |
| Network OS (NOS) | Manages network resources, provides networking services to computers connected in a network. | Windows Server, Novell NetWare, Linux Server | Server context |
• Batch OS = No real-time interaction, jobs processed in batches
• Time-Sharing = Multiple users share CPU — most common modern OS type
• Real-Time = Strict time constraints — Hard (life-critical) vs Soft (best-effort)
• Distributed = Multiple computers appear as ONE system
• Embedded = Built into devices like ATMs, microwaves
3. Microsoft Windows — Complete Version History
Windows is the most widely used desktop OS. Developed by Microsoft Corporation, founded by Bill Gates and Paul Allen in 1975. Windows uses a GUI and is the default OS on most personal computers.
| Version | Year | Key Features & Exam Notes |
|---|---|---|
| Windows 1.0 | 1985 | First version of Windows — GUI overlay on top of MS-DOS. Limited functionality. |
| Windows 3.x | 1990–1992 | Improved GUI, introduced File Manager and Program Manager. Became commercially successful. |
| Windows 95 | 1995 | Major overhaul — introduced Start Menu, Taskbar, 32-bit support, Plug and Play. Iconic. |
| Windows 98 | 1998 | Improved hardware support, introduced Internet Explorer integration, USB support. |
| Windows ME (Millennium Edition) | 2000 | Consumer version — poor stability, largely unsuccessful. |
| Windows 2000 | 2000 | Business version — very stable, based on NT kernel. |
| Windows XP | 2001 | Most loved Windows version — very stable, long support life. 32-bit and 64-bit. PYQ Favourite |
| Windows Vista | 2007 | New Aero interface — criticized for high hardware requirements and slow performance. |
| Windows 7 | 2009 | Very popular — improved over Vista, fast, stable. Many still prefer it. PYQ Favourite |
| Windows 8 / 8.1 | 2012–2013 | Removed Start Menu — added tile-based Metro UI for touchscreens. Unpopular. |
| Windows 10 | 2015 | Start Menu returned, Cortana (AI assistant) introduced, free upgrade from 7/8. Most widely used. |
| Windows 11 | 2021 | Latest version — redesigned Start Menu (centered), new UI, requires TPM 2.0 chip. |
• Windows XP and Windows 7 are most asked in PYQs
• Start Menu was introduced in Windows 95
• Windows 8 removed Start Menu — Windows 10 brought it back
• Windows 11 requires TPM 2.0 chip
• Cortana = Windows 10 AI assistant
• Windows file extension: .exe = executable file
• Windows task manager: Ctrl + Alt + Delete
4. Linux, macOS, UNIX & MS-DOS
Linux
Linux is a free, open-source operating system kernel created by Linus Torvalds in 1991. It is based on UNIX. The OS built around the Linux kernel is called a Linux Distribution (Distro).
| Linux Concept | Description |
|---|---|
| Kernel | Core component of Linux — manages hardware and system resources. Created by Linus Torvalds in 1991 |
| Shell | Interface between user and kernel — interprets user commands (text/CLI based). Examples: Bash, Zsh |
| Distributions (Distros) | Complete OS packages built on Linux kernel. Ubuntu, Fedora, Debian, CentOS, Kali Linux, Red Hat, Mint |
| Open Source | Source code is freely available — anyone can view, modify, distribute |
| Multi-User, Multi-Tasking | Multiple users can use simultaneously; supports true multitasking |
| File System | Ext4 (most common for Linux), ext3, ext2, XFS, Btrfs |
| Case Sensitive | Linux file names are CASE SENSITIVE — 'File.txt' and 'file.txt' are different files |
• Linux kernel → Linus Torvalds, 1991
• Linux is open-source and free
• Shell types: Bash (most common), Zsh, Sh, Csh
• Popular distros: Ubuntu (beginner-friendly), Red Hat (enterprise), Kali (security/hacking)
• Android is based on the Linux kernel
• Linux is case-sensitive — Windows is NOT
macOS (Apple)
macOS is Apple Inc.'s proprietary OS for Mac computers. Based on UNIX/BSD. Known for stability, security, and seamless integration with Apple devices. Current version: macOS Sequoia (2024). File system: APFS (Apple File System).
• macOS is based on UNIX/BSD
• Created by Apple Inc. (founded by Steve Jobs, Steve Wozniak, Ronald Wayne — 1976)
• File system: APFS (Apple File System) / older: HFS+
• macOS is NOT open source
• Runs only on Apple hardware
MS-DOS (Microsoft Disk Operating System)
MS-DOS was the dominant PC OS before Windows. It is a CLI-based, single-user, single-tasking OS. Developed by Microsoft in 1981 for IBM PCs.
| MS-DOS Command | Function |
|---|---|
| DIR | Lists files and directories in current directory (like 'ls' in Linux) |
| CD or CHDIR | Changes current directory. CD.. goes up one level |
| MD or MKDIR | Creates a new directory (folder) |
| RD or RMDIR | Removes/deletes an empty directory |
| COPY | Copies one or more files to another location |
| DEL | Deletes a file |
| REN | Renames a file or directory |
| CLS | Clears the screen |
| FORMAT | Formats a disk (erases all data) |
| CHKDSK | Checks disk for errors |
| ATTRIB | Displays or changes file attributes (hidden, read-only, archive) |
| TREE | Displays folder structure as a tree |
• MS-DOS = Single-user, single-tasking, CLI-based
• DIR = lists files (like Linux 'ls')
• CLS = clears screen
• CHKDSK = check disk errors
• File extension: .COM and .EXE are executable files in DOS
• Path separator in Windows/DOS: backslash \ — Linux uses forward slash /
UNIX
UNIX is the grandfather of modern operating systems. Created at Bell Labs in 1969 by Ken Thompson and Dennis Ritchie. Written in C language. macOS, Linux, Android are all UNIX-derived.
• UNIX created at Bell Labs, 1969 by Ken Thompson & Dennis Ritchie
• Written in C programming language
• UNIX = multi-user, multi-tasking
• Linux is inspired by UNIX but is NOT UNIX
• macOS IS Unix-certified (BSD-based)
5. Mobile Operating Systems
| OS | Developer & Type | Used On | Key Notes |
|---|---|---|---|
| Android | Google (Open Source — based on Linux kernel) | Samsung, OnePlus, Xiaomi, Motorola, most smartphones | Most widely used mobile OS globally. Open source — manufacturers can customise. Play Store for apps. |
| iOS | Apple Inc. (Proprietary) | iPhone, iPod Touch | Second most used. Closed ecosystem — only on Apple devices. App Store. Based on macOS/UNIX. |
| Windows Phone/Mobile | Microsoft (Discontinued) | Nokia Lumia series | Discontinued in 2017. Used tile-based UI (same as Windows 8). |
| BlackBerry OS | BlackBerry Ltd (Largely Discontinued) | BlackBerry devices | Popular for corporate/security use. Now largely replaced. |
| KaiOS | KaiOS Technologies (Based on Firefox OS) | JioPhone, basic feature phones | Lightweight OS for feature phones. Used extensively in India. |
| HarmonyOS | Huawei (Proprietary) | Huawei smartphones, tablets | Developed after Huawei was blocked from using Android. |
| Symbian | Nokia/Symbian Foundation (Discontinued) | Old Nokia smartphones | Dominant mobile OS before Android. Now obsolete. |
• Android is based on Linux kernel, developed by Google
• iOS is proprietary to Apple — only on Apple devices
• KaiOS powers JioPhone in India — Linux-based
• Windows Phone was discontinued in 2017
• Most widely used mobile OS = Android
• Android app package format: .APK
6. File Systems — FAT, NTFS, ext4 & More
A file system defines how data is stored, organised, and retrieved on a storage device. Different OS use different file systems.
| File System | Description & Key Facts | Used On |
|---|---|---|
| FAT16 / FAT32 | FAT = File Allocation Table. FAT32 is the most compatible — works on Windows, Linux, macOS. Max file size on FAT32: 4 GB. Max partition: 2 TB. Used on USB drives, SD cards. | USB drives, SD cards, older Windows, external drives |
| NTFS | New Technology File System. Windows default file system. Max file size: 16 TB. Supports file permissions, encryption, compression, journaling. | Windows XP and later — internal hard drives |
| exFAT | Extended FAT. Designed for flash drives and SD cards. Supports files larger than 4 GB (unlike FAT32). Used in modern USB drives > 32 GB. | USB flash drives >32GB, SD cards for cameras |
| ext2 / ext3 / ext4 | Linux native file systems. ext4 is current standard. Supports journaling (ext3 onwards), large file sizes, many files. | Linux internal drives — Ubuntu, Fedora, Debian |
| APFS | Apple File System — macOS and iOS default since 2017. Optimised for SSDs. Strong encryption. | macOS (2017+), iOS, iPadOS, Apple Watch |
| HFS+ | Older Apple file system (before APFS). Used in macOS before High Sierra. | Old macOS systems |
| CDFS / ISO 9660 | CD/DVD file system. Used on optical discs. | CD-ROMs, DVDs |
• FAT32 max file size = 4 GB (can't store files larger than 4GB)
• NTFS = Windows default, supports encryption & permissions
• exFAT = For large USB drives — no 4GB limit
• ext4 = Linux default file system
• APFS = Apple/macOS file system
• Windows uses backslash (\) as path separator; Linux/macOS uses forward slash (/)
7. Process Management & CPU Scheduling
A process is a program in execution. The OS manages multiple processes simultaneously through CPU scheduling algorithms.
Process States
New
Process being created
Ready
Waiting for CPU
Running
CPU executing it
Waiting/Blocked
Waiting for I/O
Terminated
Execution complete
CPU Scheduling Algorithms
| Algorithm | Description | Key Notes |
|---|---|---|
| FCFS (First Come First Served) | Processes are executed in the order they arrive. Simple but can cause 'convoy effect' — short processes wait behind long ones. Non-preemptive. | Process queue like a bank — first in, first served |
| SJF (Shortest Job First) | Process with shortest burst time is executed first. Optimal — minimum average waiting time. Can cause starvation of long processes. | Best average waiting time — non-preemptive |
| Round Robin (RR) | Each process gets a fixed time slice (quantum). After time expires, process goes back to queue. Preemptive. Most used in time-sharing systems. | Most fair — used in modern OS for multitasking |
| Priority Scheduling | Process with highest priority runs first. Can be preemptive or non-preemptive. Problem: starvation of low-priority processes. | Real-time systems, OS process prioritization |
| SRTF (Shortest Remaining Time First) | Preemptive version of SJF. Running process is preempted if a new shorter process arrives. | Optimal but complex |
| Multilevel Queue | Processes divided into separate queues by type (system, interactive, batch). Each queue has its own scheduling algorithm. | Complex systems with different process types |
• FCFS = Simplest, no starvation but poor performance
• SJF = Best average waiting time, can cause starvation
• Round Robin = Most fair, used in time-sharing OS
• Time Quantum = Fixed time slice in Round Robin
• Preemptive = OS can interrupt running process
• Non-preemptive = Process runs until it finishes or blocks
• Starvation = Low-priority process never gets CPU — solved by Aging
Multitasking, Multithreading, Multiprocessing
| Concept | Definition | Example |
|---|---|---|
| Multitasking | Multiple tasks/processes running concurrently on a single CPU. CPU switches rapidly between tasks. | Windows, Linux — modern OS |
| Multithreading | A single process is divided into multiple threads that run concurrently. Threads share the same memory space. | Web browsers — each tab is a thread |
| Multiprocessing | Multiple CPUs process different tasks simultaneously — true parallel execution. | Servers, modern multi-core processors |
| Multiprogramming | Multiple programs loaded in RAM simultaneously — CPU switches when one waits for I/O. | Early batch systems |
8. Memory Management & Virtual Memory
The OS is responsible for managing the computer's memory — deciding which programs get RAM, when, and how much.
Types of Memory
| Memory Type | Key Facts |
|---|---|
| Register | Fastest memory — inside CPU. Stores data currently being processed. Size: bytes. |
| Cache Memory | Between CPU and RAM. Stores frequently accessed data. L1, L2, L3 cache levels. |
| RAM (Primary Memory) | Main working memory — volatile (data lost on power off). Programs currently running are loaded here. |
| ROM (Primary Memory) | Read-Only Memory — non-volatile. Stores BIOS/firmware. Cannot be easily modified. |
| Virtual Memory | Uses hard disk space as an extension of RAM. Allows programs larger than RAM to run. Slower than RAM. |
| Hard Disk / SSD (Secondary) | Permanent storage — non-volatile. Stores OS, programs, files permanently. |
Virtual Memory & Paging
Virtual Memory is a memory management technique that uses a portion of the hard disk as if it were RAM. This allows the system to run programs even when physical RAM is full.
Paging
Memory divided into fixed-size blocks called pages (in virtual memory) and frames (in physical RAM). OS maps pages to frames.
Swap Space
The area of hard disk used for virtual memory is called swap space (Linux) or pagefile.sys (Windows). Swapping pages in/out of RAM is called paging.
Thrashing
When the OS spends more time swapping pages than executing processes — system slows drastically. Caused by too many processes competing for limited RAM.
• Virtual memory file in Windows = pagefile.sys
• Virtual memory in Linux = Swap partition / Swap file
• Thrashing = system too slow due to excessive paging
• Deadlock = Two processes waiting for each other's resources — neither can proceed
• RAM = volatile (data lost on shutdown). ROM = non-volatile
• Cache is faster than RAM but smaller and more expensive
9. Boot Process — From Power On to Desktop
Booting is the process of starting a computer and loading the operating system into RAM. The term comes from "pulling yourself up by your bootstraps."
| Term | Description | Notes |
|---|---|---|
| Cold Boot (Hard Boot) | Starting computer from completely powered-off state. Full POST runs. | Pressing power button from off |
| Warm Boot (Soft Boot) | Restarting computer without fully powering off. Skips some POST steps. Faster. | Ctrl+Alt+Del in Windows, Restart option |
| BIOS | Basic Input Output System — old firmware standard. Stores in ROM chip on motherboard. Manages hardware init and boot. | Traditional computers |
| UEFI | Unified Extensible Firmware Interface — modern BIOS replacement. Faster boot, supports large disks (>2TB), Secure Boot feature. | Modern computers (post-2011) |
| Secure Boot | UEFI feature — ensures only trusted, digitally signed OS can boot. Prevents malware from loading during startup. | Windows 11 requires Secure Boot |
• BIOS = Basic Input Output System = stored in ROM
• POST = Power-On Self-Test = hardware check at startup
• GRUB = Linux bootloader
• Bootmgr = Windows bootloader
• UEFI = Modern BIOS replacement — supports Secure Boot
• Windows 11 requires UEFI + TPM 2.0 + Secure Boot
• Cold Boot = from powered off | Warm Boot = restart (Ctrl+Alt+Del)
10. All JKSSB PYQs — Operating System
Actual questions from JKSSB examinations across posts — Junior Assistant, FAA, Wildlife Guard/Inspector, Panchayat Secretary, Accounts Assistant, Graduate Level, SI Finance.
11. New Statement-Based Pattern MCQs
Based on the JKSSB 2026 new pattern — evaluate multiple statements and choose the correct combination.
⚡ Quick Revision — Most Exam-Tested Facts
OS Basics
- OS = Interface between user & hardware
- MS-DOS = CLI, single-user, single-task
- Linux = Open source, Linus Torvalds 1991
- UNIX = Bell Labs, 1969, Ken Thompson
- Android = Based on Linux kernel
- macOS = Apple, based on UNIX/BSD
Windows Versions
- Start Menu → Windows 95
- Most stable/loved → Windows XP, Win 7
- Removed Start Menu → Windows 8
- Start Menu returned → Windows 10
- Needs TPM 2.0 → Windows 11
- Cortana AI → Windows 10
File Systems
- FAT32 max file = 4 GB
- NTFS = Windows default
- exFAT = Large USB drives (>32GB)
- ext4 = Linux default
- APFS = macOS (2017+)
- Windows path = \ | Linux = /
Scheduling & Boot
- Round Robin = Time-sharing, most fair
- SJF = Best avg waiting time
- FCFS = Convoy effect problem
- POST = Power-On Self-Test
- GRUB = Linux bootloader
- BIOS stored in ROM (non-volatile)
- Pagefile.sys = Windows virtual memory
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