Operating System and File Management

A computer system is made of hardware (the physical parts) and software (the programs). Software is divided into system software, which runs and manages the machine itself, and application software, which does a job for the user — a word processor, a browser, a payment app. The most important piece of system software is the operating system (OS).

An operating system is the system software that manages all the hardware and software resources of a computer and provides an interface between the user and the machine. Nothing else can run until it is loaded. Booting is the process of starting the computer and loading the operating system from secondary storage (the hard disk or SSD) into RAM (Random Access Memory), the fast temporary memory that the CPU (Central Processing Unit) works from. Starting a computer that was switched off is a cold boot; restarting one that is already on is a warm boot.

Examiners normally ask you to name the functions of an operating system and write one line on each. Learn these five in order.

• Process management. A process is a program that is currently in execution. A computer runs many processes at once, but a CPU core can attend to only one instruction stream at a time. The OS therefore schedules processes — it decides which process gets the CPU, for how long and in what order, and switches between them so quickly that they appear to run together. This is called multitasking. It also starts and ends processes and settles conflicts over shared resources.
• Memory management. The OS keeps track of every part of RAM: which part is free and which part is allotted to which program. It loads a program into memory when you open it, frees that memory when you close it, and stops one program writing into another's memory area. When RAM runs short, most operating systems use virtual memory — a reserved area of disk used as though it were extra RAM.
• File management. The OS organises data into files and folders, records where each file is physically stored, and carries out creating, opening, saving, copying and deleting. It also controls access permissions, so that one user of a shared computer cannot read another user's private files.
• Device management. Keyboard, mouse, printer, pen drive, webcam — each must be controlled. The OS does this through device drivers: small programs that translate its general instructions into the exact signals one particular device understands. It also handles spooling, for example queueing several print jobs so that users need not wait at the printer.
• Providing a user interface. The OS gives the user a way to issue commands — by typing them or by clicking on pictures. That is the subject of the next section.

Two further duties are worth a line in a long answer: security (user accounts, passwords and permissions) and error handling (noticing a failed disk read or a crashed program and reporting it instead of freezing the machine).

To remember where the OS sits: the user talks to the application, the application talks to the OS, and the OS talks to the hardware. Because it stands in the middle, it is described both as a resource manager and as an interface.

The user interface is the part of the operating system through which you give instructions and receive results. There are two families of interface, and examiners almost always ask you to compare them.

A CLI (Command Line Interface) displays a text prompt and waits for you to type a command and press Enter. The OS reads the command, carries it out and prints text output. Windows provides Command Prompt and PowerShell; Linux and macOS provide a shell inside a Terminal window. The commands differ from system to system, so always say which system a command belongs to.

Windows Command Prompt        Linux / macOS shell
----------------------------  ----------------------------
dir                           ls          (list what is here)
cd Documents                  cd Documents (change folder)
md Project                    mkdir Project (make a folder)
copy notes.txt backup.txt     cp notes.txt backup.txt
del old.txt                   rm old.txt   (delete a file)

A GUI (Graphical User Interface) shows your work on screen as pictures that you act on with a pointing device. It is summed up by the initials WIMP — Windows, Icons, Menus and a Pointer. Instead of recalling whether the copy command is copy or cp, you drag the file or right-click it and choose Copy.

The comparison an examiner wants:

• Ease of learning. A GUI is far easier for a beginner, because the available choices are visible on the screen and can be discovered by looking. A CLI must be learnt, since nothing on screen tells you which commands exist.
• Speed for a skilled user. One typed command can act on hundreds of files at once, which would need a great many clicks in a GUI.
• Repeating work. Commands can be stored in a script file and run again later, so the same job is performed identically every time. Mouse clicks cannot be saved in that way.
• Use of resources. A CLI needs very little memory and no graphics support, so it suits servers and low-powered machines; a GUI needs more RAM and more processing power.
• Risk. A mistyped delete command can remove a great deal very quickly and often gives no second chance, whereas a GUI usually asks for confirmation first.

Almost every modern system offers both.

Common desktop operating systems include Microsoft Windows, macOS from Apple, several distributions of Linux such as Ubuntu and Fedora, and ChromeOS on Chromebooks. India also has BOSS (Bharat Operating System Solutions), a Linux distribution developed by C-DAC and used in some government offices and school computer labs.

Common mobile operating systems are Android, which is built on the Linux kernel and used by many smartphone brands, and iOS, used on the iPhone. A mobile OS is designed for touch input, a small screen and a battery, so it manages power carefully and usually keeps each app inside its own storage area for safety.

Two further classifications are worth a line. Software may be proprietary — owned by a company, with the source code not published, as with Windows and macOS — or open source, where the source code is published and anyone may study, modify and redistribute it under its licence, as with Linux. Operating systems are also described as single-user or multi-user, and as single-tasking or multitasking, depending on how many people and how many programs they serve at a time.

When booting finishes, a graphical operating system shows the desktop: the main working screen on which windows, icons and the background wallpaper appear. Each item below has a proper name that you are expected to use.

An icon is a small picture that represents a file, a folder, a program or a device. Clicking or double-clicking it opens the item it stands for. A shortcut (called an alias on macOS and a symbolic link on Linux) is a special icon that only points to an item stored elsewhere. This distinction is a favourite examination question: deleting a shortcut does not delete the original file; it removes only the pointer. A shortcut icon is usually marked with a small arrow.

Along one edge of the desktop is a strip holding the button that opens the list of installed programs, buttons for running programs, and a clock and status area. It is the taskbar on Windows and most Linux desktops, and the Dock on macOS.

A window is a rectangular area of the screen in which one program or folder is displayed. Its usual parts are:

• Title bar — carries the name of the document or folder and is used to drag the window about.
• Minimise, maximise/restore and close buttons — minimise hides the window but the program keeps running in memory; maximise makes it fill the screen and restore returns it to its earlier size; close shuts the window and, on most systems, ends the program and frees its memory. Confusing minimise with close loses marks.
• Menu bar or ribbon — the lists of commands the program offers, with a toolbar of buttons for the commands used most often.
• Scroll bars — appear when the content is larger than the window, and move the view up, down or sideways.
• Status bar — a strip at the foot showing information such as page number or word count.
• Borders and corners — dragged to resize the window.

Several windows may be open at once, and you switch between them by clicking their taskbar buttons or by holding a switch key (Alt in most Windows and Linux desktops, Command on macOS) and pressing Tab. Only one window is active at a time; it receives whatever you type and usually has a highlighted title bar.

Menus are lists of commands, and their small signs carry meaning that examiners test:

• A drop-down menu opens when you click a word on the menu bar.
• A context menu (or shortcut menu) opens when you right-click an object and lists only the commands that apply to that object.
• An arrow at the right of an entry means a submenu will open.
• An ellipsis — three dots after the command name — means a dialog box will open and ask for more information before anything happens.
• A dimmed (greyed-out) entry means that command is not available at the moment, for example Paste when the clipboard is empty.
• A tick mark shows an option that is switched on; the keyboard shortcut for a command is printed beside it.

A dialog box is a small window that asks the user for information or a confirmation, such as the Save As box. Many dialog boxes are modal: you must answer or cancel them before returning to the program. Unlike a full window, a dialog box usually cannot be resized and has no minimise or maximise button.

A file is a named collection of related data stored on a secondary storage device such as a hard disk, an SSD or a pen drive. Everything you keep on a computer is a file — a letter, a photograph, a song, a spreadsheet of marks, even the programs themselves. Files are needed because RAM is volatile: its contents vanish when power is switched off, so anything you wish to keep must be written to storage.

A folder (also called a directory) is a named container used to organise files and other folders; a folder inside another folder is a subfolder. Folders hold no data of their own and take up almost no space — they merely record which items belong together. The clearest way to state the difference in an examination: a file stores data, a folder stores files and other folders.

The name of a file usually has two parts joined by a full stop — the filename and the extension. In class9-marks.xlsx, class9-marks is the name you chose and xlsx is the extension.

Naming rules vary with the operating system, so state the system if you quote a rule:

• A name may not be blank, and two items in one folder may not share exactly the same name.
• Windows does not allow the characters \ / : * ? " < > | in a filename, because the OS uses them for its own purposes.
• Case sensitivity differs. Linux treats Notes.txt and notes.txt as two different files; Windows and macOS normally treat them as the same name.
• Very long names and stray spaces are legal but awkward; hyphens or underscores are safer, especially for files that will go on a website.

The extension is the part after the last full stop. It indicates the type of data the file contains and, through a table the OS keeps called file association, which program should open it by default. Common extensions to learn:

• Text and documents: .txt plain text, .docx and .odt word processor documents, .pdf Portable Document Format, .rtf rich text.
• Spreadsheets and presentations: .xlsx, .ods, .pptx, .odp.
• Images: .jpg, .png, .gif, .bmp.
• Sound and video: .mp3, .wav, .mp4, .mkv.
• Web and programs: .html a web page, .css a style sheet, .py a Python program, .exe a program that runs directly on Windows.
• Archives: .zip, .rar, .7z — several files packed into one compressed file.

A point examiners like: renaming the extension does not convert the file. If you rename song.mp3 to song.docx, not one byte of the audio changes; the operating system is simply misled and hands the file to a word processor, which fails to read it. Real conversion needs a program that reads one format and writes the other. For the same reason, be suspicious of an attachment named photo.jpg.exe — the true extension is the last one, and this is a program, not a picture.

Every file also carries properties (or attributes) that the OS maintains: its size in KB or MB, the dates it was created and last modified, its location, and flags such as read-only (it can be opened but not overwritten) and hidden (not shown unless you ask). Right-clicking a file and choosing Properties or Get Info shows them.

Folders are arranged in a hierarchical structure — a tree. The topmost point of the tree is called the root. On Windows each storage device receives a drive letter, so the root of the main disk is C:\ and a pen drive may appear as E:\. On Linux and macOS there is a single tree whose root is written /, with other devices attached inside it. The separator between folder names is the backslash \ on Windows and the forward slash / on Linux and macOS.

Here is a small tree:

C:\
|-- Users
|   |-- Anita
|       |-- Documents
|       |   |-- Projects
|       |       |-- report.docx
|       |-- Pictures
|           |-- logo.png
|-- Windows

A path is the address that tells the operating system where a file or folder lies in this tree. There are two kinds.

An absolute path (also called a full path) states the complete route from the root, naming every folder along the way. For the file above:

C:\Users\Anita\Documents\Projects\report.docx        (Windows)
/home/anita/Documents/Projects/report.docx           (Linux)

An absolute path is unambiguous: it identifies exactly one file, and it means the same thing whichever folder you happen to be working in. You can recognise it because it begins with a drive letter and a backslash on Windows, or with a forward slash on Linux and macOS.

A relative path states the route from the current working directory — the folder you are in at that moment. It does not begin at the root. Two special names are used:

• . (a single dot) means this folder, the current folder.
• .. (two dots) means the parent folder, one level up.

Suppose the current folder is C:\Users\Anita\Documents. Then:

• Projects\report.docx refers to the same report — go down into Projects and take the file.
• ..\Pictures\logo.png means go up one level to C:\Users\Anita, then down into Pictures and take logo.png.
• ..\..\ would move up two levels, to C:\Users.

Each kind has its own advantage, and examiners ask for one of each:

• An absolute path works from anywhere and never becomes ambiguous, which is why it is used in settings files and in system commands.
• A relative path is shorter to write and, more importantly, stays valid if the whole folder is moved or copied elsewhere, because the internal arrangement of the folder does not change.

That second point is the reason relative paths are used inside web pages. If a page stores its pictures in a subfolder called images, it refers to one as images/logo.png. Copy the entire site folder to a pen drive or to a web server, and every such link still works. Had the page used the absolute path C:\Users\Anita\site\images\logo.png, every picture would break the moment the site left that computer. Paths written inside web pages always use forward slashes, whatever the operating system.

Two smaller points. A file's full name is really its path plus its filename, which is why two files may share the name notes.txt provided they sit in different folders. And a file manager — File Explorer on Windows, Finder on macOS, Files on many Linux desktops — shows the current path in an address bar.

Creating. A folder is made by right-clicking an empty part of a folder window, choosing New and then Folder, and typing a name; at a command line the instruction is md or mkdir. A file is normally created by an application: you type your work and choose Save As, which asks for a filename, a folder and sometimes a file type. Note the distinction — Save silently writes over the existing file, while Save As creates a fresh copy under a new name or place, leaving the earlier one untouched.

Renaming. Select the item and choose Rename from the context menu, or press the rename key your system uses (F2 on most Windows computers). Take care not to disturb the extension: if the file manager is set to hide extensions you may not even see it. Renaming changes only the label, never the contents.

Copying and moving. These two are constantly confused, so learn them precisely.

• Copy makes a duplicate. The original stays where it was, so afterwards two copies exist.
• Move (Cut) relocates the item. It disappears from the source folder, so afterwards only one copy exists.

Both work through the clipboard, a temporary area of RAM holding whatever was last cut or copied until something replaces it. On most Windows and Linux desktops the shortcuts are Ctrl+C copy, Ctrl+X cut and Ctrl+V paste; macOS uses Command in place of Ctrl. Because the clipboard lives in RAM, its contents are lost when the computer is shut down. Dragging with the mouse also works, but its meaning varies — within one drive a drag usually moves the item, to a different drive it usually copies — so cut/copy and paste are safer.

To act on several files at once, Ctrl+click scattered items, click the first and Shift+click the last for a whole run, or press Ctrl+A for everything in the folder.

Deleting and the Recycle Bin. Pressing Delete does not usually erase a file. It moves the file to a special folder — the Recycle Bin on Windows, the Trash on macOS and most Linux desktops — from which it can be restored to its original location. Three consequences are examined regularly:

• A file in the Recycle Bin still occupies disk space. The space is released only when you empty the bin or delete the item from inside it.
• Holding Shift while pressing Delete on most Windows systems removes the file permanently, bypassing the bin after a warning.
• Files deleted from a pen drive, a memory card or a network drive are usually not placed in the bin, because the bin belongs to the computer's own disk. They are gone at once, so check twice before deleting from removable media.

On Windows the bin also has a size limit, and once it is full the oldest items are discarded to make room. The Recycle Bin is a safety net against a careless click, never a backup.

Searching. Every file manager has a search box, and most modern operating systems keep an index of filenames so that results appear quickly. You can search on part of a name and narrow the result with filters for date modified, size, file type or location. Two wildcard characters make a search exact:

• * stands for any number of characters, including none. *.jpg finds every JPEG image; report* finds every name beginning with report.
• ? stands for exactly one character. chap?.txt matches chap1.txt and chap7.txt, but not chap12.txt and not chap.txt.

Finally, a folder's contents can be sorted by name, date modified, size or type. Sorting by date modified is the quickest way to find yesterday's file when you cannot recall its name.

Compression means reducing the size of a file, or of a group of files, so that it takes less storage space and less time to transfer. The tool packs the chosen files into a single archive, usually with the extension .zip, .rar or .7z. Most operating systems can create and open ZIP archives without extra software: select the files, right-click and choose the compress option. Opening the archive again is called extracting or unzipping, and it recreates the original files and folder arrangement.

There are two kinds of compression, and the difference is examined:

• Lossless compression stores the same information in a cleverer way, so that on extraction the original is recovered exactly, byte for byte. Nothing is thrown away. ZIP archives and PNG images use lossless methods. Compression must be lossless for documents, spreadsheets and programs, where one changed byte could ruin the file.
• Lossy compression permanently discards detail that eyes or ears are unlikely to notice, in exchange for a much smaller file. JPEG photographs, MP3 audio and MP4 video are lossy. The discarded detail can never be recovered, and re-saving the same JPEG repeatedly slowly degrades its quality.

How much a file shrinks depends on what is inside it. Plain text and spreadsheets compress a great deal, because they contain much repetition; JPEG photographs and MP4 videos barely shrink, because those formats are already compressed. Zipping still helps there, because it bundles many files into one attachment and keeps the folder structure intact.

Backups. A backup is an additional copy of your data, kept separately, so that it can be restored if the original is deleted by mistake, corrupted, stolen, destroyed by hardware failure or locked by malicious software. The essential word is separately: a second copy on the same disk protects you from a careless click, but not from that disk failing.

• A full backup copies all the selected data every time. It is simple and quick to restore, but slow to make and large.
• An incremental backup copies only what has changed since the previous backup. It is fast and small, but restoring means replaying the last full backup and the increments in order.
• Backup media include an external hard disk, a pen drive, a writable disc and cloud storage — space on a provider's computers, reached over the internet. Official Indian certificates can also be kept in DigiLocker.
• A widely taught rule of thumb: keep three copies of anything important, on two kinds of media, with one stored in a different physical place.

Safe file handling is the set of habits an examiner expects you to list:

• Save your work often, and use Save As to keep dated versions such as science-project-2026-08-06.docx; a date written year-month-day sorts correctly by name.
• Give files and folders meaningful names, organise them by subject, and avoid special characters and stray spaces.
• Scan any pen drive with antivirus software before opening files from it, and never run an unexpected attachment — the last extension is the real one.
• Use Safely Remove Hardware or Eject before pulling out a pen drive, so the operating system finishes writing; pulling it out mid-write commonly corrupts files.
• Password-protect confidential documents, and never keep scans of an Aadhaar card, a bank passbook or similar identity papers in a shared folder — such documents are exactly what identity thieves look for.
• Mark master copies read-only so they cannot be overwritten by accident, and keep the computer on a UPS so a power cut does not interrupt a save.
• Never treat the Recycle Bin as a backup: it sits on the same disk, has a size limit, and is emptied without warning by clean-up tools.