Class 10 Computer Science Chapter 1 Complete Guide Book — Operating Systems: Structure and Services | PunjabTest.com

An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs. It works as a bridge (middle layer) between the user and the computer hardware: the user gives instructions, and the OS makes the hardware carry them out.

OS as the central controller: The OS controls the CPU, memory, storage and devices, decides which program runs when, and keeps programs from disturbing each other. Without an OS, every program would have to talk to the hardware directly, which would be slow and unsafe.

Multi-user environment: In schools, offices and online systems many people may use the same computer. The OS ensures: the creation and management of separate user accounts; each user's files and information stay private; resources are shared fairly so one user does not slow down the system; and shared resources are protected from unauthorised access.

The architecture of an operating system is the way its parts are organised and how they work together. Two parts matter most:

Kernel: The kernel is the core part of the OS. It directly controls the hardware and system software such as the CPU, memory and devices, and decides how and when programs may use these resources. Example: when you open a file, the kernel manages reading it from the hard disk and sending it to the screen. Think of the kernel as the engine of a car.

Shell: The shell is the outer part of the OS that interacts with the user. It receives commands from the user and passes them to the kernel. There are two kinds: graphical shells (like the Windows desktop, where you click icons and use menus) and command-line shells (like Command Prompt or Terminal, where you type instructions). The shell is like the car's steering wheel and dashboard — the part you touch.

Layers and modular design: In operating systems the design is divided into layers, each with a specific job. The lower layer works directly with hardware devices like the CPU, RAM and hard disk. The middle layer manages these resources and makes sure programs can use them when needed. The upper layer runs applications and provides the interface the user sees on the screen. Each layer depends on the one below it, which makes the OS easier to manage, repair and improve without changing the whole system.

School example: Support staff (guards, cleaners) work at the base keeping the school ready — like lower layers working with hardware. The administration manages resources, schedules and rules — like middle layers managing memory and storage. Teachers and students use these arrangements to teach and learn — like upper layers running applications.

System libraries are collections of ready-made instructions that programs can use for common tasks, such as opening files or showing text on the screen. Example: a photo app uses the OS library to read an image instead of inventing its own method. Device drivers are special programs that allow the OS to communicate with hardware devices such as printers, keyboards and graphics cards.

A process is a program in execution — for example, your browser running, or a game loading. Process management is the OS job of creating processes, scheduling them on the CPU, switching between them, and ending them when they finish or fail.

Because the CPU can truly do one thing at a time, the OS gives each process a short turn (a time slice) and switches rapidly, so many programs appear to run together. This is multitasking. The OS also handles process states: a process may be new, ready, running, waiting (for example waiting for a file or key press), or terminated.

Threads: A thread is a smaller unit inside a process — a single path of execution. One process can have several threads doing different parts of the job at once (for example, a browser thread loading a page while another plays a video). Threads of the same process share its memory, so switching between threads is cheaper than switching between whole processes. Process vs thread: a process is a whole running program with its own memory; a thread is a lightweight part of a process that shares that memory.

Memory management is how the OS keeps track of the computer's memory (mainly RAM), gives each program the memory it needs, and takes it back when the program ends. RAM is fast but limited and temporary — everything in it is lost when power goes off.

The OS must: keep a record of which parts of memory are free and which are in use; allocate memory to processes when they start; protect one process's memory from another's (so a faulty program cannot corrupt others); and free memory when a process ends, so it can be reused. When RAM runs short, the OS may move less-used data to a special area on the disk (virtual memory / swap space) and bring it back when needed — slower, but it lets more programs run than RAM alone would allow.

Why it matters for you: Opening too many heavy programs at once slows the computer because RAM fills up and the OS spends time swapping data to disk. Closing unused programs frees memory and speeds things up again.

A system call is the way a program asks the operating system (kernel) to do something it cannot do itself — for example, read a file, print a document, create a process, or use the network. The program makes the call, the kernel performs the privileged work, and the result is returned to the program. System calls are the controlled doorway between applications and hardware: programs never touch hardware directly.

The file system is how the OS organises data on storage. Files are grouped into folders (directories) in a tree-like (hierarchical) structure, each file has a name, location (path), size and permissions, and the OS handles creating, opening, reading, writing, renaming, moving and deleting files. It also tracks where each file's data actually sits on the disk, so that a file can be found again even though its pieces may be stored in different places.

Permissions matter: File permissions decide who may read, write or run a file. This protects your work: another user account on the same computer cannot freely open or change your private files.

Operating systems are grouped by how they serve users and jobs:

Common real systems: Windows, macOS and Linux (desktop/laptop), Android and iOS (mobile). Linux is open-source; Windows and macOS are commercial. A good board answer names the type and explains why it fits the situation.