Operating System Notes for SSC Exams

Operating system (OS) is a core topic of SSC Computer Knowledge. Every exam has at least one question on the functions of an OS, its types or examples such as Windows, Linux and Android. These operating system notes for SSC explain the topic with tables, key facts and practice questions. Read it along with the Computer Memory Notes and Computer Shortcut Keys notes.

What Is an Operating System?

An operating system is system software that manages the hardware and software of a computer and works as a bridge between the user and the computer. Without an OS, a computer cannot run any application.

• An OS is the first program loaded into the memory when the computer starts.
• It provides a user interface to give commands.
• It controls the CPU, memory, storage and input and output devices.

Functions of an Operating System

Function	What it does
Process management	Decides which program gets the CPU and when
Memory management	Allocates and frees the main memory for programs
File management	Creates, stores, copies and deletes files and folders
Device management	Controls input and output devices through drivers
Security	Protects data with passwords and permissions
User interface	Provides a GUI or a command line to the user

Types of Operating Systems

Type	Meaning	Example
Batch OS	Similar jobs are collected and run together without user interaction	Early IBM mainframes
Time-sharing (multi-user) OS	Many users share the CPU time	Unix
Multitasking OS	Runs many programs at the same time	Windows, Linux
Multiprocessing OS	Uses more than one CPU	Modern servers
Real-time OS (RTOS)	Responds within a fixed time	Air traffic control, missile systems
Network OS	Manages the computers on a network	Windows Server
Mobile OS	Runs on phones and tablets	Android, iOS

Popular Operating Systems

OS	Fact
Windows	Made by Microsoft; Windows 1.0 came in 1985; GUI based; Windows 11 was released in 2021
Linux	Open-source; kernel created by Linus Torvalds in 1991; Ubuntu is a Linux distribution
Unix	Multi-user OS developed at Bell Labs
macOS	Made by Apple for Mac computers
Android	Made by Google; based on the Linux kernel; open source
iOS	Made by Apple for iPhones
MS-DOS	Command-line OS by Microsoft

Kernel, Shell and User Interface

• The kernel is the core part of the OS that talks directly to the hardware.
• The shell is the part that takes the commands from the user and passes them to the kernel.
• GUI (Graphical User Interface) uses icons, windows and menus. Example: Windows.
• CUI or CLI (Command Line Interface) uses typed commands. Example: MS-DOS, Linux terminal.

Booting

Booting is the process of starting the computer and loading the OS into the RAM. Cold boot means starting a computer that is switched off. Warm boot means restarting a computer that is already on. When the power is on, the BIOS (stored in ROM) runs the POST (Power-On Self Test) to check the hardware, then it loads the OS from the hard disk into the RAM. The program that loads the OS is called the bootstrap loader.

History of Operating Systems

Period	Development
1950s	Early computers had no OS; programs were loaded by hand; batch processing began
1960s	Time-sharing and multiprogramming; Unix development began at Bell Labs (1969)
1980	Microsoft bought 86-DOS in 1980 and supplied it as MS-DOS for the IBM PC (1981)
1984	Apple Macintosh introduced a GUI-based OS
1985	Windows 1.0 launched as a GUI on top of MS-DOS
1991	Linus Torvalds released the Linux kernel
1995	Windows 95 with the Start button and taskbar
2007-08	iOS and Android were released for smartphones
2015 and 2021	Windows 10 and Windows 11

Process Management and CPU Scheduling

• A program is a set of instructions kept on the disk. A process is a program in execution.
• A process moves through the states: new, ready, running, waiting (blocked) and terminated.
• The CPU scheduler decides which ready process gets the CPU next. Common algorithms are First Come First Served (FCFS), Shortest Job First (SJF), Round Robin and Priority scheduling.
• In Round Robin, every process gets a fixed time slice (time quantum), which is the base of time-sharing systems.
• Multithreading means a process has many threads (small units of work) that run together.
• A deadlock happens when two or more processes wait for each other forever for the resources they hold.

Memory Management Terms

• Paging divides the memory into fixed-size blocks called pages and frames.
• Segmentation divides the memory into variable-size parts according to the logic of the program.
• Virtual memory uses a part of the hard disk as if it were RAM, so that large programs can run.
• Thrashing happens when the system spends more time on swapping data than on running programs.
• Spooling (Simultaneous Peripheral Operations On-Line) keeps the data in a queue, such as the print queue, so the CPU does not wait for a slow printer.

File System and Disk Terms

Term	Meaning
FAT32	An older Windows file system; a single file is limited to 4 GB
NTFS	The modern Windows file system with security and large file support
ext4	A common Linux file system
Directory (folder)	A container that holds files
Path	The address of a file, absolute or relative
Formatting	Preparing a disk for use and creating a file system
Partition	A logical section of a disk, shown as a drive such as C: or D:

More About Popular Operating Systems

OS	Developer	Important point
Windows	Microsoft	Most used desktop OS; paid; GUI; closed source
macOS	Apple	Runs on Mac computers; based on Unix
Linux	Linus Torvalds and the community	Free and open source; used in servers, supercomputers and Android; distributions are Ubuntu, Fedora, Debian and Red Hat
Unix	AT&T Bell Labs (Ken Thompson and Dennis Ritchie)	Multi-user and multitasking; the base of many OSs
Android	Google	Most used mobile OS; the kernel is Linux; apps are .apk files
iOS	Apple	Mobile OS only for Apple devices
Chrome OS	Google	Light OS based on the Chrome browser
BOSS	C-DAC (India)	Bharat Operating System Solutions, an Indian Linux-based OS
Maya OS	Indian defence organisations	Ubuntu-based OS developed in India for the defence sector

Types of Operating Systems in More Detail

• Single-user, single-tasking OS runs one program at a time (early MS-DOS).
• Single-user, multitasking OS lets one user run many programs, such as Windows on a PC.
• Multi-user OS lets many users use the same computer at the same time, such as Unix and Linux servers.
• Distributed OS manages a group of independent computers so that they look like one system.
• Embedded OS runs in machines such as ATMs, routers and washing machines.
• Real-time OS has two types: hard real-time (a missed deadline is a failure, such as in missile systems) and soft real-time (a small delay is allowed, such as in video streaming).

Important Questions Explained

Question 1: Which software acts as a bridge between the user and the hardware?
Answer: The operating system.

Question 2: Who created the Linux kernel?
Answer: Linus Torvalds, in 1991.

Question 3: Which OS is based on the Linux kernel and made by Google?
Answer: Android.

Question 4: What is the process of loading the OS into the memory called?
Answer: Booting.

Question 5: Which type of OS responds within a fixed time limit?
Answer: A real-time operating system (RTOS).

Question 6: Which part of the OS communicates directly with the hardware?
Answer: The kernel.

Quick Tips to Remember

• Learn the functions of the OS as a list of six: process, memory, file, device, security, user interface.
• Remember Windows with GUI, MS-DOS with CUI and Linux with open source.
• Link Linus Torvalds with Linux and Microsoft with Windows.
• Learn that warm boot means restart and cold boot means starting from off.
• Remember the shell as the command interpreter and the kernel as the core.

Common Mistakes to Avoid

• Writing MS Word as an operating system.
• Confusing the kernel with the shell.
• Mixing the cold boot and the warm boot.
• Thinking Android is made by Apple.
• Writing Windows as an open-source OS.

Quick Revision Points

• OS = system software that manages hardware and software.
• Functions: process, memory, file, device, security management.
• Windows = Microsoft, Linux = Linus Torvalds, Android = Google.
• Kernel is the core; shell is the command interpreter.
• Booting loads the OS into the RAM; POST checks the hardware.

Practice Questions With Answers

1. Which of these is an operating system?
   Answer: Linux (MS Word is application software).
2. Who developed the Linux kernel?
   Answer: Linus Torvalds (In 1991).
3. Which company developed Windows?
   Answer: Microsoft (GUI based).
4. Which OS is used in most smartphones and is made by Google?
   Answer: Android (Based on Linux).
5. What does GUI stand for?
   Answer: Graphical User Interface (Uses icons and windows).
6. What is the first step in booting?
   Answer: POST (Power-On Self Test) (Checks the hardware).
7. Which OS is open-source?
   Answer: Linux (Free to modify).
8. Which OS is command-line based?
   Answer: MS-DOS (CUI).
9. What is restarting a running computer called?
   Answer: Warm boot (Cold boot is from power off).
10. Which part of the OS interacts with the hardware?
    Answer: Kernel (Core of the OS).

More Practice Questions With Answers

1. Who created Unix?
   Answer: Ken Thompson and Dennis Ritchie (Bell Labs).
2. What is a program in execution called?
   Answer: Process (Not just a file).
3. Which scheduling gives a time slice to each process?
   Answer: Round Robin (Time-sharing).
4. What is it called when processes wait for each other forever?
   Answer: Deadlock (Resource waiting).
5. Which Windows file system is modern and secure?
   Answer: NTFS (FAT32 is older).
6. Which OS was developed by C-DAC in India?
   Answer: BOSS (Bharat Operating System Solutions).
7. Which technique keeps the print jobs in a queue?
   Answer: Spooling (Printer).
8. What is the logical section of a disk called?
   Answer: Partition (C: and D:).
9. Which OS runs in ATMs and routers?
   Answer: Embedded OS (Fixed tasks).
10. Which OS is based on the Chrome browser?
    Answer: Chrome OS (Google).
11. Which type of OS is used in missile systems?
    Answer: Hard real-time OS (Deadline critical).
12. What is the time given to each process in Round Robin called?
    Answer: Time quantum (Time slice).

How to Practise This Chapter

1. Read the tables once and learn the key facts by heart.
2. Revise the quick revision points the next day.
3. Attempt the practice questions above without looking at the answers.
4. Solve a full SSC CGL Tier 1 mini mock to test your general awareness.
5. Check the previous year papers to see how SSC asks computer questions.

Related Notes and Practice Papers

• Computer Memory Notes
• Input and Output Devices Notes
• Computer Shortcut Keys
• Computer Knowledge Notes for SSC
• SSC CGL Tier 1 Mini Mock

Explore More SSC Subjects

SSC exams test many subjects, so connect this topic with the related subjects below:

• General Science Notes
• General Awareness Notes
• Quantitative Aptitude Notes
• Reasoning Notes
• Electrical Engineering (SSC JE) Notes
• All SSC subjects and notes

Frequently Asked Questions

What is an operating system?

An operating system is system software that manages the hardware and software of a computer and lets the user run programs.

What are the main functions of an operating system?

Process management, memory management, file management, device management, security and providing a user interface.

Name some popular operating systems.

Windows, Linux, Unix, macOS, Android and iOS.

What is the difference between a kernel and a shell?

The kernel is the core of the OS that controls the hardware, while the shell takes commands from the user and passes them to the kernel.

What is a GUI?

A GUI is a graphical user interface that uses icons, windows and menus, such as Windows.

What is booting?

Booting is the process of starting the computer and loading the operating system into the RAM.

What is the difference between cold and warm boot?

A cold boot starts a computer from the switched-off state, while a warm boot restarts a running computer.

Which operating system is open source?

Linux and Android (based on the Linux kernel) are open source.

How many questions come from operating systems in SSC exams?

One or two questions usually come from operating systems.

What is the difference between a program and a process?

A program is a set of instructions stored on the disk, while a process is a program that is running in the memory.

What is a deadlock?

A deadlock is a situation in which two or more processes wait for each other forever because each holds a resource that the other needs.

What is virtual memory?

Virtual memory is a technique that uses a part of the hard disk as an extension of the RAM so that larger programs can run.