Computer Software and Operating System

Hardware is the part of a computer you can hit with a hammer; software is the part you can only swear at. Strip the software out of a laptop and you are left with an expensive brick — silicon that can switch voltages but has no idea what to switch them to. This unit looks at the instructions that bring the machine to life: how software is classified, what an operating system does, how to work confidently inside Windows, and why Linux and Android now run most of the world's computers.

3.1 Definition of software and its categories

Software is intangible: it has no weight and no moving parts, it does not wear out, and it is copied for almost nothing. It does, however, "rot" in the sense that it must be updated as hardware, standards and security threats change.

1. System software controls and coordinates the hardware and provides a platform on which application software runs. It includes the operating system, language translators (compiler, interpreter, assembler), device drivers and system utilities. It is normally supplied by the hardware or OS vendor.

2. Utility software (service programs) performs housekeeping tasks that keep the system healthy: antivirus, disk defragmenter, disk cleanup, backup and restore, file compression (WinRAR, 7-Zip), and disk partitioning tools. Utility software is strictly a sub-class of system software, but the NEB syllabus lists it separately because it is what a user actually notices.

3. Application software is written to solve a user's problem rather than to run the machine. It splits into:

• General purpose (packaged) software — sold ready-made to everybody: MS Word, MS Excel, Photoshop, VLC, Chrome.
• Tailor-made (custom or bespoke) software — written for one organisation: the billing system of Nepal Electricity Authority, a school's own result processing program.

4. Web-based software runs on a remote server and is used through a browser, so nothing is installed on your machine. Examples: Gmail, Google Docs, Google Sheets, Facebook, Canva, GitHub, and government portals such as the online passport and PAN registration systems. This model is also called SaaS (Software as a Service).

5. Mobile applications (apps) are written for smartphones and tablets, are touch-first and battery-aware, and are distributed through stores such as Google Play and the Apple App Store. Examples used daily in Nepal include eSewa, Khalti, Nagarik App, Pathao, Hamro Patro and IMEPay.

Category	Purpose	Installed where	Examples
System software	run and manage the hardware	on the machine	Windows 11, Linux, device drivers, compilers
Utility software	maintain and protect the system	on the machine	antivirus, disk cleanup, WinRAR, backup
Application software	do the user's work	on the machine	MS Word, Excel, Photoshop, VLC
Web-based software	do the user's work online	on a remote server	Gmail, Google Docs, Canva, Facebook
Mobile apps	do the user's work on a handset	on the phone	eSewa, Khalti, WhatsApp, Nagarik App

3.2 Introduction, role and functions of an operating system

Without an OS, every program would have to contain its own code for reading a keyboard, drawing on a screen and writing to a disk. The OS provides these services once, for everybody.

Role of the operating system

• As a resource manager it decides which program gets the CPU, how much memory each one receives, and in what order printing jobs are served.
• As an extended (virtual) machine it hides the ugly detail of the hardware behind simple commands such as "open this file".
• As an interface it gives the user a command line or a graphical desktop through which to give instructions.

Functions of the operating system

1. Process management — creates, schedules, suspends and terminates processes; allocates CPU time; handles deadlocks and inter-process communication.
2. Memory management — keeps track of which parts of main memory are free, allocates memory to processes, protects one process from another and implements virtual memory so that programs larger than RAM can run.
3. File management — creates, opens, reads, writes, renames and deletes files; organises them into directories; keeps track of free disk space; and enforces file permissions.
4. Device (I/O) management — communicates with every peripheral through its device driver, maintains buffers and queues, and implements spooling so that a slow printer does not hold up the CPU.
5. Security and protection — user accounts, passwords, access rights, encryption and a firewall; keeps one user's data away from another's.
6. User interface and job control — provides the CLI or GUI and the means to start, stop and monitor jobs.
7. Error detection and system performance monitoring — reports hardware faults and keeps statistics such as CPU and memory usage (Task Manager).

OS type	Response required	Typical use	Example
Batch	none (jobs grouped, run later)	payroll, billing runs	early IBM mainframe OS
Single-user, single-task	immediate	very old desktops	MS-DOS
Multi-user, time-sharing	fast, fair	servers, university systems	UNIX, Linux
Real-time	guaranteed deadline	ATMs, robots, medical devices	RTOS, VxWorks
Distributed	fast, over a network	cloud, clusters	Linux clusters
Embedded / mobile	immediate, low power	phones, TVs, routers	Android, iOS

3.3 OS terminology: multiprogramming, multitasking, multiprocessing and distributed processing

These four words are constantly confused. The distinguishing questions are: how many jobs are in memory?, how many CPUs are there?, and how many computers are involved?

Multiprogramming. Several programs are loaded in main memory at once, but there is only one CPU. Whenever the running program stops to wait for a slow input or output operation, the OS gives the CPU to another program. The aim is to keep the CPU busy and maximise throughput. A program keeps the CPU until it blocks; it is not forcibly interrupted.

Multitasking (time sharing). A refinement of multiprogramming in which the OS also forcibly takes the CPU away after a fixed time slice (a few milliseconds) and gives it to the next task in turn. Because the switching is so fast, the user believes that Word, Chrome and VLC are all running at once. The aim is fast response time. Multitasking may be co-operative (the program yields voluntarily, as in old Windows 3.x) or pre-emptive (the OS decides, as in every modern system).

Multiprocessing. A single computer contains two or more processors (or cores) that execute instructions genuinely simultaneously. Work really is done in parallel, so speed and reliability both improve — if one processor fails the others carry on. Every modern phone and laptop is a multiprocessing system.

Distributed processing. Several independent computers, each with its own CPU and memory, are connected by a network and co-operate on one problem under the control of a distributed operating system. The user sees a single system. Examples: cloud data centres, computing clusters, and the servers behind eSewa or a bank's core banking system.

	Number of CPUs	Number of computers	Switching trigger	Main aim
Multiprogramming	one	one	job waits for I/O	CPU utilisation
Multitasking	one	one	time slice expires	response time
Multiprocessing	two or more	one	no switching — true parallelism	speed, reliability
Distributed	many	many	job split over the network	scale, resource sharing

3.4 Windows OS: a GUI based OS and its features

A GUI (Graphical User Interface) lets the user work with pictures — windows, icons, menus and a pointer — instead of typed commands. The four elements are often abbreviated WIMP. Microsoft Windows, first released in 1985 and now at Windows 11 (mainstream support for Windows 10 ended in October 2025), is the most widely used desktop GUI operating system in the world; as of 2025 it holds roughly 70 % of the desktop market, with macOS and Linux (including ChromeOS) sharing most of the rest.

CLI (command line)	GUI (graphical)
Commands are typed exactly	Objects are clicked or tapped
Must memorise the command set	Options are visible on screen
Very little memory and CPU needed	Needs much more memory, CPU and a graphics adapter
Very fast for an expert; scriptable	Slower for bulk work, but easy for a beginner
Examples: MS-DOS, Linux bash, PowerShell	Examples: Windows 11, macOS, GNOME, Android

Features of Windows

• Desktop metaphor with icons, wallpaper, taskbar and Recycle Bin.
• Multitasking and multi-user support with separate accounts and profiles.
• Plug and Play — a newly connected device is detected and its driver installed automatically.
• File Explorer for a hierarchical view of drives, folders and files.
• Snap layouts, virtual desktops and Task View for arranging many windows (Windows 10 and 11).
• Built-in security: Windows Hello sign-in, Microsoft Defender antivirus, Windows Firewall, BitLocker drive encryption and User Account Control.
• Accessibility: Narrator, Magnifier, high-contrast themes, speech recognition.
• OneDrive cloud integration, Microsoft Store, and Windows Update.
• Support for a huge range of hardware and legacy software — the main reason Windows still dominates offices in Nepal.

3.5 Working in a desktop application and the window environment

A window is a rectangular area of the screen in which one application runs. Every Windows application window has the same furniture, so once you can drive one you can drive them all.

Part of the window	What it does
Title bar	shows the document and program name; drag it to move the window
Control buttons	minimise (to taskbar), maximise / restore, close
Menu bar / ribbon	groups every command of the program into tabs
Toolbar / quick access	one-click buttons for common commands (save, undo)
Work area	where the document, image or web page is displayed
Scroll bars	move the view vertically or horizontally
Status bar	shows page number, word count, zoom level, mode
Border and corners	drag to resize the window

Working with windows. Move a window by dragging its title bar; resize by dragging a border; maximise by double-clicking the title bar or pressing Windows + Up; snap two windows side by side by dragging one to the left or right edge (or Windows + Left / Windows + Right); switch between windows with Alt + Tab; see all open windows and virtual desktops with Windows + Tab; minimise everything with Windows + D.

3.6 Managing files and folders with File Explorer

File Explorer (Windows + E) is the Windows tool for browsing that tree. Its parts are the navigation pane on the left (Quick access, This PC, OneDrive, Network), the ribbon or command bar at the top, the address bar showing the current path, the search box, and the content pane listing the items.

Common file-management operations

Task	How to do it
Create a folder	right-click empty space → New → Folder, type the name, press Enter
Rename	select, press F2, type the new name
Copy	select, Ctrl + C, open the destination, Ctrl + V
Move	select, Ctrl + X, open the destination, Ctrl + V (or drag within the same drive)
Delete to Recycle Bin	select, press Delete
Delete permanently	select, press Shift + Delete
Restore a deleted file	open Recycle Bin, right-click the item → Restore
Select several items	Ctrl + click for scattered items, Shift + click for a run, Ctrl + A for all
Search	type in the search box; use *.docx to find all Word files
See hidden files	View → Show → Hidden items
Check size / properties	right-click → Properties

A file is identified by its name and its extension, separated by a dot. The extension tells Windows which program should open the file.

Extension	Type of file	Usual program
.docx	word processor document	MS Word
.xlsx	spreadsheet workbook	MS Excel
.pptx	presentation	MS PowerPoint
.pdf	portable document	Adobe Reader, browser
.txt	plain text	Notepad
.jpg .png	image	Photos
.mp3 .mp4	audio, video	media player
.exe	executable program	Windows itself
.zip .rar	compressed archive	File Explorer, WinRAR

3.7 Customising the Start screen and desktop; installing and removing devices

Customising the desktop

Right-click the desktop → Personalise to reach the settings for:

• Background — a picture, a solid colour or a slideshow.
• Colours — light or dark mode, accent colour, transparency.
• Themes — a saved bundle of wallpaper, colours, sounds and mouse pointers.
• Lock screen and screen saver (with "on resume, display logon screen" for security).
• Taskbar — alignment (centre or left), which icons appear, auto-hide, combine buttons.
• Display settings (right-click the desktop) — resolution, orientation, scaling, multiple monitors, night light.

Desktop icons are added through Personalise → Themes → Desktop icon settings (This PC, Recycle Bin, Network) or by right-clicking a program → Send to → Desktop (create shortcut).

Customising the Start menu

Open Settings → Personalisation → Start to choose whether recently added apps, most used apps and recommended files are shown. To pin a program, right-click it in the Start menu or in the app list and choose Pin to Start (or Pin to taskbar); to remove it choose Unpin from Start. Tiles or icons can be dragged into a new position and grouped into folders.

Installing and removing devices

Most hardware today is Plug and Play: plug the device into a USB port and Windows identifies it, finds a matching driver and configures it automatically. If it does not:

1. Connect the device and switch it on.
2. Open Settings → Bluetooth & devices → Add device (for a Bluetooth or wireless device), or Settings → Bluetooth & devices → Printers & scanners → Add device for a printer.
3. If no driver is found, install the driver supplied by the manufacturer on a disc or downloaded from the manufacturer's website.
4. Verify in Device Manager (right-click Start → Device Manager) that the device is listed without a yellow warning triangle.

To remove a device: right-click Start → Device Manager, right-click the device → Uninstall device, tick delete the driver software if you want it gone completely, then unplug the hardware. A USB flash drive should always be removed through Safely Remove Hardware in the notification area so that any buffered data is written out first.

To uninstall a program, go to Settings → Apps → Installed apps, click the three dots beside the program and choose Uninstall (the old route was Control Panel → Programs and Features).

3.8 Managing passwords and privacy; Control Panel, system tools and accessories

User accounts, passwords and privacy

Windows supports several account types: Administrator (can install software and change system settings), Standard user (can run programs and change only personal settings), and Guest / Child accounts with further restrictions. Accounts are managed from Settings → Accounts.

To change a password: Settings → Accounts → Sign-in options → Password → Change. Other sign-in options include a PIN, Windows Hello face or fingerprint recognition, and a picture password.

Privacy levels are set in Settings → Privacy & security, where you decide which apps may use the camera, microphone, location, contacts and notifications, how much diagnostic data is sent to Microsoft, and whether an advertising ID is used. Related security settings live in Windows Security: virus and threat protection, firewall, account protection, and device encryption (BitLocker). User Account Control (UAC) asks for confirmation before any program makes a system-wide change.

Control Panel

The Control Panel is the classic central place for configuring Windows. It is opened by typing control in the search box, and its main categories are:

Category	Typical settings
System and Security	system information, Windows Tools, backup, BitLocker
Network and Internet	network status, adapter settings, internet options
Hardware and Sound	devices and printers, power options, sound, AutoPlay
Programs	uninstall a program, default programs, Windows features
User Accounts	change account type, Credential Manager
Appearance and Personalisation	fonts, File Explorer options, taskbar
Clock and Region	date, time, time zone, formats
Ease of Access	Narrator, Magnifier, high contrast

In Windows 11 most of these are being migrated into the modern Settings app, but the Control Panel is still present and is still examinable.

System tools and accessories

Tool	What it does
Disk Cleanup	deletes temporary files, cached pages and Recycle Bin contents
Disk Defragmenter / Optimise Drives	rearranges fragmented files on a hard disk so reads are faster (not used on SSDs, which are "trimmed" instead)
Backup and Restore / File History	copies important files so they can be recovered
System Restore	returns system files and settings to an earlier restore point
Task Manager (Ctrl + Shift + Esc)	shows running processes, CPU, memory, disk and network usage; ends a hung program
Disk Management	creates, formats, shrinks and extends partitions
Device Manager	lists hardware and manages drivers
Windows Security	antivirus, firewall, threat history
Character Map	inserts symbols not on the keyboard
Notepad / WordPad	simple text editing
Paint	simple drawing and image editing
Calculator	standard, scientific, programmer (base conversion!) and date modes
Snipping Tool	captures part of the screen
Command Prompt / PowerShell / Terminal	command line access

3.9 Open source operating systems: UNIX, Linux and Linux distributions

Advantages: no licence fee; the code can be inspected, so security holes are found and fixed quickly; it can be customised for local needs (for example Nepali language support); it is not tied to one vendor; and it often runs well on older hardware.

Disadvantages: commercial support may have to be bought separately; some proprietary hardware lacks drivers; specialised commercial software (certain accounting or engineering packages) may not be available; and the user interface varies between distributions.

UNIX

UNIX was developed at AT&T Bell Laboratories in 1969 by Ken Thompson and Dennis Ritchie, and was rewritten in the C language in 1973 — which is why it could be moved from one machine to another. UNIX is a multi-user, multitasking, time-sharing operating system with a hierarchical file system, a powerful shell and the philosophy of "small tools that do one job well and can be piped together". It is proprietary; modern descendants include IBM AIX, Oracle Solaris, HP-UX and (through BSD) macOS.

Linux

Linux is a free, open-source, UNIX-like operating system kernel written by Linus Torvalds in 1991 while he was a student in Helsinki, and released under the GNU GPL. Combined with the GNU tools of Richard Stallman's GNU Project (begun in 1983) it forms a complete operating system, properly called GNU/Linux. As of 2025 Linux runs essentially all of the world's top 500 supercomputers, the large majority of web servers and cloud instances, and — through the Android kernel — most of the world's smartphones.

The kernel is the core of Linux: it manages processes, memory, devices and the file system. The shell (bash, zsh, fish) is the command interpreter that reads what you type and asks the kernel to carry it out. Some everyday shell commands:

pwd                  print the working directory
ls -l                list files with details
cd /home/sabina      change directory
mkdir Class11        make a directory
cp notes.txt backup/ copy a file
mv old.txt new.txt   rename or move
rm -i notes.txt      remove, asking first
cat marks.txt        display a file
chmod 755 run.sh     change file permissions
sudo apt update      run a command as the superuser
man ls               read the manual page

Linux distributions

A distribution (distro) is the Linux kernel packaged together with GNU utilities, a desktop environment, a package manager and a collection of applications, ready to install.

Distribution	Family / package manager	Best known for
Ubuntu	Debian, apt	the easiest starting point; huge community
Debian	Debian, apt	rock-solid stability; the base of many others
Linux Mint	Debian/Ubuntu, apt	a familiar Windows-like desktop
Fedora	Red Hat, dnf	newest technology; upstream of RHEL
Red Hat Enterprise Linux / CentOS Stream	Red Hat, dnf	paid commercial support in servers
openSUSE	SUSE, zypper	the YaST configuration tool
Arch Linux	Arch, pacman	build-it-yourself, rolling release
Kali Linux	Debian, apt	penetration testing and security tools

Feature	Windows	Linux
Source code	closed, proprietary	open, GPL
Cost	paid licence	normally free
File system	NTFS, drive letters C: D:	ext4, one tree from /
Path separator	backslash \	forward slash /
Case sensitivity	file names not case sensitive	file names are case sensitive
Superuser	Administrator	root (reached with sudo)
Software source	Store, .exe installers	package manager repositories
Typical use	desktops, offices	servers, supercomputers, embedded, Android

3.10 Mobile operating systems and their types

Differences from a desktop OS: a touch-first interface; aggressive power management; each app is sandboxed and must request permissions; apps are installed from a controlled app store; the system must survive interruptions such as an incoming call; and memory and storage are limited and not user-upgradeable.

Mobile OS	Owner	Kernel / base	Open source?	Notes
Android	Google (Open Handset Alliance)	Linux	yes (AOSP core)	largest share; used by Samsung, Xiaomi, Oppo, Vivo; apps from Google Play
iOS / iPadOS	Apple	Darwin (UNIX-like)	no	runs only on Apple hardware; App Store only; strong privacy record
HarmonyOS	Huawei	HarmonyOS/Linux	partly	developed after Huawei lost Google services; large in China
KaiOS	KaiOS Technologies	Linux	partly	for cheap feature phones with 4G
Wear OS / watchOS	Google / Apple	Linux / Darwin	no	smart watches
Windows Phone	Microsoft	Windows NT	no	discontinued in 2019 — historical only
Symbian, BlackBerry OS	Nokia / BlackBerry	—	no	dominant before 2010; now obsolete

As of 2026 the current major releases are Android 16 and iOS 26. Two operating systems therefore account for almost the entire market, which is why mobile application developers normally target only Android and iOS — or write one cross-platform app with a framework such as Flutter or React Native.

Chapter summary

• Software is the set of programs that tells hardware what to do. The syllabus categories are system, utility, application, web-based and mobile apps.
• An operating system is the interface between user and hardware and the manager of all resources. Its functions are process, memory, file, device, security and user-interface management.
• Multiprogramming: many jobs, one CPU, switch on I/O wait. Multitasking: many jobs, one CPU, switch on time slice. Multiprocessing: many CPUs in one machine, true parallelism. Distributed: many machines on a network acting as one.
• Windows is a GUI (WIMP) operating system whose desktop, taskbar, Start menu, windows and File Explorer follow one consistent design. Know the parts of a window and the standard file operations and shortcuts.
• A file path names a drive, the chain of folders and the file with its extension, for example D:\Class11\Computer\notes.docx.
• Control Panel and Settings configure the system; system tools such as Disk Cleanup, Task Manager, Device Manager and System Restore maintain it.
• Open source means the source code is published and may be modified. UNIX (Bell Labs, 1969) is the ancestor; Linux (Torvalds, 1991) is the free UNIX-like kernel, delivered as distributions such as Ubuntu, Debian, Fedora and Mint.
• Mobile operating systems are touch-first, power-aware and sandboxed. Android (Linux based, open) and iOS (Apple, closed) together hold almost the whole market.

Practice questions

Group A — Multiple choice (1 mark each)

1. Which of the following is not system software? [1]adevice driverbcompilercMS Exceldoperating system
2. Google Docs is an example of [1]autility softwarebweb-based softwarecsystem softwaredfirmware
3. The part of the operating system that is always resident in main memory is the [1]ashellbkernelccompilerddriver
4. Executing several programs on a single CPU by giving each a fixed time slice is called [1]amultiprogrammingbmultiprocessingcmultitaskingdbatch processing
5. Which key combination opens File Explorer in Windows? [1]aWindows + DbWindows + EcCtrl + Shift + EscdAlt + Tab
6. Linux was first developed by [1]aDennis RitchiebRichard StallmancLinus TorvaldsdBill Gates
7. Which of the following is a Linux distribution? [1]aFedorabSolariscDarwindSymbian
8. Android is based on which kernel? [1]aWindows NTbDarwincLinuxdSymbian
9. The tool used to remove temporary files and free disk space is [1]aDisk CleanupbDevice ManagercTask ManagerdCharacter Map

Answers to Group A

1. (c) — MS Excel is application software.

2. (b) — it runs on a remote server and is used through a browser.

3. (b) — the kernel.

4. (c) — the fixed time slice is the mark of multitasking.

5. (b) — Windows + E.

6. (c) — Linus Torvalds, 1991.

7. (a) — Fedora; Solaris and Darwin are UNIX-like but not Linux, and Symbian was a mobile OS.

8. (c) — Linux.

9. (a) — Disk Cleanup.

Group B — Short answer (5 marks each)

1. Define software. Explain the five categories of software given in the syllabus with two examples of each. [5]
2. What is an operating system? Explain any five functions of an operating system. [5]
3. Differentiate between multiprogramming and multitasking, and between multiprocessing and distributed processing. [5]
4. What is a GUI? List any six features of the Windows operating system and compare a GUI with a CLI. [5]
5. Write the steps to create a folder named Project on drive D, copy two files into it, rename one of them, and delete the other permanently. [5]
6. What is open source software? Write any four advantages of it and name four Linux distributions. [5]

Answers to Group B

1. Software is a set of programs, procedures and documentation that tells hardware what to do. System: Windows 11, device drivers. Utility: antivirus, WinRAR. Application: MS Word, Photoshop. Web-based: Gmail, Google Docs. Mobile apps: eSewa, Khalti.

2. An OS is system software that acts as an interface between the user and the hardware and manages all resources. Five functions: process management, memory management, file management, device (I/O) management, and security and protection. (User-interface provision and error detection also earn the mark.)

3. Multiprogramming vs multitasking — both keep several programs in memory on one CPU, but multiprogramming switches only when the running program waits for I/O and aims at CPU utilisation, whereas multitasking switches after a fixed time slice and aims at response time. Multiprocessing vs distributed — multiprocessing uses two or more CPUs inside one computer sharing one memory; distributed processing uses many independent computers with their own memory linked by a network.

5. (i) Windows + E → This PC → Local Disk (D:). (ii) Right-click empty space → New → Folder → type Project → Enter. (iii) Select the two files, Ctrl + C, open D:\Project, Ctrl + V. (iv) Click the first file, press F2, type the new name, Enter. (v) Click the second file and press Shift + Delete, then confirm — this bypasses the Recycle Bin.

6. Open source software publishes its source code under a licence allowing anyone to run, study, modify and redistribute it. Advantages: no licence cost; security flaws are found and fixed quickly because the code is public; it can be customised (for example for Nepali); no vendor lock-in. Distributions: Ubuntu, Debian, Fedora, Linux Mint (also openSUSE, Arch, Kali).

Group C — Long answer (8 marks each)

1. (a) Define an operating system and explain its role as a resource manager and as an extended machine. [3](b) Explain in detail any five functions of an operating system, and name one Windows tool associated with each. [5]
2. (a) With a suitable diagram, explain the parts of a window in a Windows application. [4](b) Explain the steps to install a new printer, and the steps to uninstall an unwanted program from a Windows computer. [4]
3. (a) What is open source software? Compare Windows and Linux under any five headings. [5](b) What is a mobile operating system? Explain any three types with their owners and note how a mobile OS differs from a desktop OS. [3]

Answers to Group C

1. (b) Process management — scheduling the CPU among processes (Task Manager). Memory management — allocating RAM and virtual memory (Task Manager → Performance). File management — creating, organising and protecting files (File Explorer). Device management — drivers, buffering and spooling (Device Manager). Security — accounts, passwords, firewall, antivirus (Windows Security). Each point should be explained in two or three sentences with an example.

2. (b) Installing a printer: connect the printer by USB or to the Wi-Fi network and switch it on → Settings → Bluetooth & devices → Printers & scanners → Add device → Windows searches and installs the driver → if it is not found, click Add manually and supply the driver from the manufacturer's disc or website → print a test page. Uninstalling a program: Settings → Apps → Installed apps → find the program → click the three dots → Uninstall → confirm, and restart if asked. (Control Panel → Programs and Features does the same job.)

3. (b) A mobile OS is an operating system for handheld devices, designed for a touch screen, limited battery and cellular connectivity. Android (Google, Linux kernel, open source, apps from Google Play); iOS (Apple, Darwin kernel, closed, runs only on Apple hardware); HarmonyOS (Huawei) or KaiOS (for feature phones). Differences from a desktop OS: touch-first interface, strict power management, sandboxed apps with permissions, app-store-only installation, and hardware that cannot be upgraded by the user.