Class 10 Computer Science Notes – Chapter 1: Operating Systems: Structure and Services

A. Multiple-Choice Questions (MCQs)

1. Which is NOT an example of an operating system?

(a) Linux
(b) Windows
(c) Photoshop
(d) macOS

Correct Answer: (c) Photoshop

2. In multi-user environments, the OS ensures:

(a) Equal access and data privacy
(b) All users share the same files
(c) Hardware is never used
(d) Internet speed is increased

Correct Answer: (a) Equal access and data privacy

3. In Windows, user accounts can be created via:

(a) Task Manager
(b) Control Panel or Settings
(c) Disk Management
(d) System Settings

Correct Answer: (b) Control Panel or Settings

4. The core part of the OS that interacts directly with hardware is the:

(a) Shell
(b) Kernel
(c) Device Driver
(d) BIOS

Correct Answer: (b) Kernel

5. A graphical shell allows the user to:

(a) Type commands only
(b) Click icons and use menus
(c) Interact only via code
(d) Access only the BIOS

Correct Answer: (b) Click icons and use menus

6. In the FCFS scheduling method, processes are served:

(a) Randomly
(b) Shortest job first
(c) In the order they arrive
(d) By priority only

Correct Answer: (c) In the order they arrive

7. Threads in the same process:

(a) Have separate memory spaces
(b) Share the same memory and resources
(c) Run on different operating systems
(d) Cannot run simultaneously

Correct Answer: (b) Share the same memory and resources

8. Which system call is used to create a new process?

(a) open
(b) read
(c) write
(d) fork

Correct Answer: (d) fork

B. Short Questions

1. Why is the operating system referred to as the “central controller”?

The OS acts like a traffic controller that manages all hardware components, allocates CPU time, manages computer memory, and controls active peripheral devices, such as printers or speakers, to ensure the system runs smoothly.

2. How does the OS act as a translator between the user and hardware?

Computer hardware works with binary language (0s and 1s), whereas humans use languages like Urdu or English. The OS converts user actions, such as clicking or typing, into machine-understandable instructions and displays the results back to the user.

3. Define one way to create a new user account in Windows.

In Windows, a new user account can be created by opening Settings or Control Panel, navigating to User Accounts, selecting Add New User, and providing a username, password, and account type.

4. How is the kernel different from the shell?

Kernel: The core inner part of the OS that directly interacts with and manages hardware, including the CPU, RAM, and storage.
Shell: The outer interface of the OS that interacts directly with the user through a command-line interface (CLI) or graphical user interface (GUI) to receive commands and forward them to the kernel.

5. Give one example of a system library and its purpose.

A system library provides ready-made instructions for common tasks. For example, when a photo viewer application needs to open an image, it calls an OS system library to handle reading the image file from storage instead of writing custom code for file opening.

6. Explain one advantage and one disadvantage of FCFS scheduling.

Advantage: It is simple to understand and implement because tasks are processed in the exact order they arrive, without skipping any process.
Disadvantage: Short processes can be delayed significantly if they arrive behind a long-running process. This is known as the convoy effect.

7. Why is virtual memory slower than RAM?

Virtual memory uses space on secondary storage drives, such as HDDs or SSDs. Storage drives operate at much lower data transfer speeds and have higher latency and access times compared to primary RAM.

8. Define a system call.

A system call is a program’s request to the operating system kernel to perform specific low-level or hardware-related operations that user applications cannot execute directly.

9. What is the role of a file system?

A file system organizes, stores, tracks, and manages files and folders on physical storage devices so that data can be located, retrieved, and kept secure.

10. Define multitasking in a computer system.

Multitasking allows an OS to keep multiple programs open and actively usable for a user at the same time, allowing seamless switching between tasks.

C. Long Questions

1. Describe the architecture of an operating system, explaining kernel, shell, and layered design with examples.

The architecture of an OS organizes its internal components into clear functional parts.

Kernel

The kernel is the foundational core component that interacts directly with physical hardware, including the CPU, memory, storage, and input/output devices. It manages system resources safely.

Example: It works like the engine of a car.

Shell

The shell is the user-facing software interface that interprets user commands and forwards them to the kernel. Shells can be command-line interfaces, such as Terminal or Command Prompt, or graphical interfaces, such as the Windows Desktop.

Example: It works like a car’s dashboard and steering wheel.

Layered Design

The system architecture is divided into modular layers, each having a distinct role.

Lower Layer: Works directly with physical hardware components.
Middle Layer: Handles resource management, including memory allocation, process scheduling, and the file system.
Upper Layer: Executes application programs and provides user interface displays.

Example analogy: In a school, support staff act as lower layers by maintaining the physical grounds. Administration acts as the middle layer by allocating rooms and schedules. Teachers and students act as upper layers by carrying out academic activities.

2. Explain the process lifecycle in detail with examples.

A process is a program currently under execution. It passes through three main lifecycle stages.

Creation → Execution → Termination

1. Creation

Occurs when a user launches an application, such as by clicking Google Chrome.
The OS loads the program binary into memory and allocates the necessary resources, including CPU priority and memory blocks.

2. Execution

The process actively uses CPU cycles to run code instructions, load webpages, render media, or process user inputs.

3. Termination

Occurs when the program finishes its work or is closed by the user or system.
The OS halts execution and releases the allocated RAM and other resources back to the available resource pool.

3. Differentiate between RAM and virtual memory, and explain how multithreading improves performance.

Difference between RAM and Virtual Memory

Feature	Primary Memory (RAM)	Virtual Memory
Type	Main physical semiconductor memory	Portion of secondary storage (SSD/HDD) used as RAM
Speed	Extremely fast data access	Slower due to storage drive latency
Capacity	Limited physical capacity	Extends the available memory pool when RAM fills up
Volatility	Volatile; data is lost when powered off	Temporary space managed on storage media

How Multithreading Improves Performance

Multithreading divides a single process into smaller concurrent execution units called threads that share memory space. It improves performance in the following ways:

Responsiveness: Enables an application to remain interactive, such as typing in a document while a background thread runs spellcheck.
Parallel Processing: Executes subtasks across CPU cores concurrently.
Resource Efficiency: Requires fewer system overhead resources than creating separate individual processes.

4. Describe system calls, their purpose, and give examples of at least three types.

System Call and Purpose

A system call acts as a secure programmatic interface between user applications and the OS kernel. Because application code cannot directly control hardware for security reasons, it uses system calls to request the kernel to perform protected operations.

Types and Examples of System Calls

1. open

Requests the OS to open an existing file or create a new file for reading or writing.

Example: Opening a video file in a media player.

2. read

Retrieves stored data bytes from a file or hardware input device into memory.

Example: Reading the text contents of a document.

3. write

Sends processed data bytes from memory to an output device or disk file.

Example: Saving an image file to disk.

4. fork

Creates a new child process by cloning an existing parent process.

Example: The supplied notes give opening a new tab in a web browser as an example.

5. Numerical Problem: First-Come, First-Served (FCFS) Scheduling

Given Table

Process	Arrival Time (s)	Burst Time (s)
P1	0	4
P2	1	3
P3	2	1

Solution

I. Execution Order

Since FCFS processes jobs in the exact order of arrival:

[
P_1 \rightarrow P_2 \rightarrow P_3
]

II. Execution Timeline (Gantt Chart)

P1 runs from 0 s to 4 s.
P2 runs from 4 s to 7 s.
P3 runs from 7 s to 8 s.

Gantt Chart:

[P1: 0–4] → [P2: 4–7] → [P3: 7–8]

III. Start Time and Completion Time

P1: Starts at 0 s and completes at 4 s.
P2: Starts at 4 s and completes at 7 s.
P3: Starts at 7 s and completes at 8 s.

IV. Calculation of Waiting Time

[
\text{Waiting Time}=\text{Start Time}-\text{Arrival Time}
]

Waiting time for P1:

[
0-0=0\text{ seconds}
]

Waiting time for P2:

[
4-1=3\text{ seconds}
]

Waiting time for P3:

[
7-2=5\text{ seconds}
]

V. Average Waiting Time

[
\text{Average Waiting Time}=
\frac{WT(P_1)+WT(P_2)+WT(P_3)}{3}
]

[
=\frac{0+3+5}{3}
=\frac{8}{3}
\approx 2.67\text{ seconds}
]

Final Answer: Average waiting time = 2.67 seconds

Notes by Sir Dilawar

For more notes, visit QuranEducationPoint.com