Unit 1: Operating Systems: Structure and Services — Long Questions

Ans. ★ Key Points Operating System | Central System Controller

1. Introduction to Operating System (OS)
Operating System (OS) is a type of system software that manages hardware, runs application software, and provides a user interface, like Windows, macOS, Linux, Android, and iOS, along with their basic roles.

2. Operating System (OS) as the Central System Controller
An operating system works like a traffic controller for the computer. It decides which task should be done first, how the computer's memory is used, and which devices (like a printer or speakers) should be active at a given time. In short, we can say that the OS makes sure the computer works smoothly even when multiple tasks are running at the same time.

Ans. ★ Key Points OS Role in Hardware Interaction | Multiuser | Managing User Accounts.

1. Role in User-Hardware Interaction
Computer hardware cannot understand human language directly. The operating system acts as a translator between the user and the hardware system.

Example When you click an icon or type something, the OS changes those actions into instructions that the hardware can understand. This allows people to use computers easily without learning how the hardware works.

2. Responsibilities in Multi-User Environments Tasks
In places like schools, offices, or online systems, many people may use the same computer. The operating system ensures:

• The creation and management of separate user accounts.
• Keeps each user's files and information private.
• Shares the computer's resources fairly so that no one slows down the systems functionalities.
• Protect shared resources from unauthorized access.

3. Creating and Managing User Accounts
The operating system allows separate accounts for different users, each with its own desktop, files, settings, and passwords.

Example In computer lab, student login with a username and password provided by the school. This keeps each student's work separate and private. In most modern OS like Windows, a new account can be created through the Settings or Control Panel by selecting User Accounts, choosing Add New User, and entering details like username, password, and account type (Standard, Administrative, Guest).

Ans. ★ Key Points OS Architecture | Layers in OS

1. Architecture of an Operating System
The architecture of an operating system is the way how its parts are organized and how they work together. Each part has a special role, and together they make the computer work smoothly just like a school has different departments that perform specific duties but work together for the smooth working of the school.

2. Kernel vs Shell

a. Kernel: The kernel is the core part of the operating system. That directly controls the computer's system software and hardware such as the CPU, memory, and devices, as shown in figure. It decides how and when different programs can use these resources.

Example When you open a file, the kernel manages the process of reading it from the hard drive and sending it to the screen. Like the engine of a car work is kernel and accessories like steering wheel, dashboard is shell.

b. Shell: The shell is the outer part of the OS that interacts with the user, also depicted in figure. It receives commands from the user and passes them to the kernel. Shells can be:
i. Graphical shells (like Windows desktop) where you click icons and use menus.
ii. Command-line shells (like the Command Prompt or Terminal) are where you type instructions.

3. OS Layers and Modular Design
In operating systems, the design is divided into layers, where each layer has a specific job:
a. Lower layer: Work directly with hardware devices like the CPU, RAM and hard drive.
b. Middle layer: Manages these resources and makes sure programs can use them when needed.
c. Upper layer: Run applications and provide the interface that the user views on the screen.

Each layer depends on the one below it. This design makes the operating system easier to manage, repair, and improve without changing the whole system.

Example A school system can be used as an example to understand the layered architecture of an operating system:

• The support staff (like guards and cleaners) work at the base, keeping the school ready (like the lower layers working with hardware).
• The administration manages resources, schedules, and rules (like the middle layers managing memory and storage).
• The teachers and students use these arrangements to teach and learn (like the upper layers running applications and interacting with users).

Ans. ★ Key Points System Libraries | Device Drivers

System Libraries and Device Drivers
System libraries are collections of ready-made instructions that programs can use to perform common tasks, such as opening files or showing text on the screen.

Example When a photo editing app needs to open an image, it uses the operating system's library to read the file. This way, the app does not have to create its own method for opening pictures. Device drivers are special programs that allow the operating system to communicate with hardware devices such as printers, keyboards, and graphics cards.

Ans. ★ Key Points Process Management | Process Life cycle | Multitasking | Concurrency

The operating system is responsible for managing all the programs that run on a computer. In this context, these running programs are called processes. Process management ensures that each process gets the resources it needs, even when multiple processes are active. Process management is one of the most important jobs of an operating system because it ensures all processes run smoothly without disturbing each other.

1. Process Life Cycle
A process goes through several stages during its life cycle:

a. Creation
i. This happens when you start any program (like MS Word).
ii. The OS loads the program into memory and gives it the resources (like CPU time and memory) it needs.

b. Execution
i. The process is actively running and performing tasks effectively.

c. Termination
i. The process finishes its task and is closed by the user or the system.
ii. The OS release the resources so they can be used by other processes.

Example Process Life cycle of opening a Web Browser on your mobile or computer like Google Chrome.
a. Creation: Begins when the user clicks the browser icon. The operating system loads the program into memory and allocates the required resources.
b. Execution: The browser performs tasks such as loading web pages, displaying media, and responding to user actions.
c. Termination: Occurs when the browser is closed. The operating system stops the process and releases its resources for other uses.

2. Multitasking and Concurrency
Modern operating systems can manage many processes so efficiently that it appears they are all running at the same time.

a. Multitasking: The operating system allows more than one program to be open and usable by a single user at the same time. You can easily switch between them whenever you need.

Example You can listen to music, keep a document open, and browse the internet, moving between them as needed.

b. Concurrency: More than one process is active at the same time in an OS, but the CPU processes them one by one in extremely fast cycles.

Example Like a chef preparing three dishes, working on one for a short time, then moving to the next, and repeating, the CPU switches between processes so rapidly that the user does not notice any delay.

3. Process Scheduling Concepts
We know that many processes can be in progress during the same time period, but the CPU works on them one at a time in very fast turns. Since the CPU cannot run all processes at the same time, the operating system must decide:

• Which process should run first?
• How long each process should run?

This process is called scheduling. There are different scheduling methods used by operating systems. First Come, First Served (FCFS), which is the simplest scheduling techniques.

Ans. ★ Key Points Process Scheduling Concepts | Merits & Demerits

There are different scheduling methods used by operating systems. First Come, First Served (FCFS), which is the simplest scheduling techniques. In the FCFS method, the CPU processes tasks in the exact order they arrive. The first process to arrive is completed first, and the next process starts only after the previous one finishes.

Example Like a queue at a shop counter, the first customer in line is served first, then the next, and so on.

Numerical Example Let us use some simple data to see how FCFS scheduling works in practice.

Process ID | Arrival Time | Time Needed
P1 | 0 seconds | 5 seconds
P2 | 1 second | 3 seconds
P3 | 2 seconds | 2 seconds

1. Step-by-Step Explanation
a. At 0 seconds

• P1 arrives first, so it starts running immediately.
• It requires 5 seconds to finish.
• It runs from 0s to 5s.

b. At 1 second

• P2 arrives while P1 is still running, so P2 waits.

c. At 2 seconds

• P3 arrives, but P1 is still running and P2 is already waiting.
• In FCFS, P3 will also wait until both P1 and P2 have completed.

d. At 5 seconds

• P1 finishes.
• The CPU now starts P2, which needs 3 seconds to complete.
• P2 runs from 5s to 8s.

e. At 8 seconds

• P2 finishes.
• The CPU now starts P3, which needs 2 seconds.
• P3 starts and runs from 8s to 10s.

Execution Timeline
[ P1 0-5] → [ P2: 5-8] → [ P3: 8-10]
0 5 8 10

P1 0s - 5s (finish at 5)
P2: 5s - 8s (finish at 8)
P3: 8s - 10s (finish at 10)

2. Observation
Even though P3 has the shortest duration (only 2 seconds), it must still wait until P1 and P2 have finished because they arrived earlier. This is one of the main characteristics of FCFS; short tasks can be delayed if they arrive after longer ones.

3. Advantages and Disadvantages of FCFS
Although FCFS is a simple and fair scheduling method, it has both advantages and disadvantages:

a. Advantages

• Easy to understand and implement
• Processes are served in the exact order they arrive.
• No process is skipped.

b. Disadvantages

• Short processes may have to wait a long time if they are queued behind longer processes.
• It can affect the overall efficiency of the system.

Ans. ★ Key Points Memory | RAM | Virtual Memory

Memory is a fundamental component of a computer system, used to store data and instructions temporarily required for processing. It ensures that the CPU can access information quickly during program execution.

1. Primary Memory (RAM)
Primary memory, also called Random Access Memory (RAM) or Volatile Memory, is the main working area of a computer. It is a fast storage area where the computer keeps the data and instructions temporarily. Its data is erased when the computer is turned off.

Example When you open a Word document, the computer quickly places the program and the document into RAM so the CPU can work on them right away.

2. Virtual Memory
When the RAM is full, the operating system uses part of the computer's storage drive (like Hard Disk Drives (HDD), Solid-State Drives (SSD), or Non-Volatile Memory Express (NVMe)) as virtual memory. This extra space acts like temporary RAM, allowing more programs to run at the same time. Storage drives operate at lower data transfer speeds and have higher access times as compared to RAM; that's why the use of virtual memory can result in reduced system performance. When several programs are open simultaneously, the operating system may transfer data from less active programs to virtual memory. This frees up space in RAM for the programs you are currently using, but may make those fewer active programs slower to respond.

Ans. ★ Key Points Processes | Threads

Processes An independent program that is currently being executed by the computer. It has its own memory space, CPU time, and other resources (files, network). Processes are isolated from one another to ensure stability and security. A problem in one process does not affect another. A web browser as a whole is one process.

Threads The smallest unit of execution within a process. Shares the same memory and resources within the process. Threads operate independently but are not isolated; they share resources. Allows multiple tasks within the same process to run simultaneously without waiting for each task to finish. Loading a webpage, playing audio/video, and downloading files are threads within the browser process.

Ans. ★ Key Points Multithreading | Merits of Multithreading

Multithreading is an operating system technique that allows a single process to perform multiple tasks at the same time by dividing its work into smaller units called threads. Each thread runs independently but shares the same memory and resources of the process, enabling faster execution, better responsiveness, and efficient use of system resources.

Benefits of Multithreading
Multithreading offers several advantages, and some of the most important are discussed below:

1. Enhanced Performance: Tasks can be divided into multiple threads and executed in parallel, allowing complex operations to complete more quickly and improving overall system efficiency.

2. Improved Responsiveness: Applications remain responsive even when one thread is busy with a specific task.

Example A word processor enables continuous typing while another thread check spelling in the background.

3. Support for Concurrent (parallel) Operations: Multiple tasks can progress during the same period, which is particularly important in applications such as games, video editing, and real-time communication tools.

4. Efficient Use of Resources: Threads share the same memory space and resources of their parent process, requiring fewer system resources compared to creating separate processes.

Ans. ★ Key Points System Call | open | read | write | fork

A system call is a request made by a program to the operating system to perform a specific task that the program cannot do directly.

1. Purpose: They act as a bridge between user programs and the kernel, allowing applications to access hardware and core OS functions safely. Without system calls, programs that directly control hardware can be unsafe and complex.

Example When you save a file in a text editor, the program uses a system call to tell the operating system to write the data to the storage drive (like a Hard drive).

2. Types of System Calls: The main types of system calls include:

a. open: Opens a file for reading or writing.
Example: Opening a music file to play.

b. read: Retrieves data from a file or input device.
Example: Reading text from a document.

c. write: Sends data to a file or output device.
Example: Saving an image to the computer

d. fork: Creates a new process by duplicating an existing one.
Example: Opening a new browser tab, where the OS may use fork to create another process.

Ans. ★ Key Points File Structure | File Management | Files | Folders | Metadata | File Systems

An operating system not only runs programs but also stores and organizes the user's data. This is achieved through the file system, which provides a structured way for users and applications to store, locate, and manage information on storage devices. A well-designed file system ensures that data remains organized, secure, and easily retrievable, even when there are thousands of files containing complex data.

1. Files
A file is a collection of related data stored on a computer. It may contain text, images, audio, video, or program instructions.

2. Folders
A folder (also called a directory) is a container used to organize files and other folders in a logical structure, making it easier to locate and manage information.

3. Metadata
Metadata refers to details about a file folder, such as its name, type, size, date of creation, and date of last modification. This information helps both the operating system and the user identify and manage files/folders without opening them.

4. File Systems
A file system is the way an operating system stores and organizes files on a storage device, such as a hard drive, SSD (Solid State Drive), or USB (Universal Serial Bus). It decides where each file will be kept and saves its location so it can be accessed later. Some widely used file systems are including computer-based file systems are including:

a. FAT 32 (File Allocation Table 32): Used in USB flash drives
b. NTFS (New Technology File System): Used by Windows OS.
c. APFS (Apple File System): Used by macOS.
d. EXT4 (Fourth Extended File System): Commonly used by Linux OS.

The choice of file system affects performance, storage capacity, and security features.

Example If you save a photo on your computer, the file system makes sure it is stored in the right place and knows exactly where to find it when you open it again, just like a librarian placing a book in the right section and knowing where to locate it later.

Ans. ★ Key Points Real-Time Operating System | Embedded Operating System | Network Operating System | Mobile Operating System

Operating systems are designed according to the needs of the device and the work it performs. Each type serves a different purpose and is optimized for specific tasks.

1. Real-Time Operating System (RTOS)
A Real-Time Operating System is designed to process data and respond within a strict time limit, known as a deadline. It is used where even a tiny delay can cause system failure or serious consequences.

a. Key Feature: Processes tasks immediately as they arrive, without long waiting times.
b. Used in: Critical systems such as air traffic control, heart-monitoring devices, or industrial robots.

2. Embedded Operating System (EOS)
An Embedded OS is a small and highly efficient operating system built into a specific device to control only the functions it needs. It is not meant for general purpose computing but is optimized for one task or a small set of tasks.

a. Key Feature: Uses very little memory and power, and is often stored permanently inside the device.
b. Used in: Home appliances (microwaves, washing machines), printers, smart TVs (Television), and ATMs (Automated Teller Machine).

3. Network Operating System (NOS)
A Network OS manages and supports multiple computers connected through a network. It enables the sharing of resources like files, printers, and internet connections among users like windows multipoint servers.

a. Key Feature: Focuses on communication and coordination between computers.
b. Used in: Offices, schools, and data centers.

Example In a school computer lab, students use different computers, but all can save files to the same server and print from the same printer.

4. Mobile Operating System
A Mobile OS is designed for smartphones, tablets, and other handheld devices. It is optimized for touch-screen use, battery saving, and mobile apps.

a. Key Feature: Supports wireless connectivity, cameras, sensors, and app stores.
b. Used in: Smartphones, tablets, smartwatches.