Day 1 – Introduction to Operating Systems

1. Definition

An Operating System (OS) is a software layer between the user and the hardware that manages resources and provides an environment for programs to execute.

2. Main Objectives

1. Resource Management – Manage CPU, memory, I/O devices.

2. Process Management – Schedule and execute processes.

3. File Management – Store, organize, and control access to data.

4. Security & Protection – Control access to resources.

5. User Interface – Provide CLI (Command-Line Interface) or GUI (Graphical User Interface).

3. Types of Operating Systems

• Batch OS – Jobs are processed in batches without user interaction.

• Multiprogramming OS – Multiple programs loaded in memory, CPU switches between them.

• Multitasking OS – Multiple tasks executed by sharing CPU time.

• Multiprocessing OS – Multiple CPUs work together.

• Real-Time OS (RTOS) – Gives output within strict deadlines.

• Distributed OS – Multiple computers connected, appearing as a single system.

• Time-Sharing OS – CPU time is divided among users.

4. Functions of OS

1. Process Management – Scheduling, creation, termination of processes.

2. Memory Management – Allocation, deallocation, paging, segmentation.

3. File System Management – File creation, deletion, permissions.

4. I/O System Management – Input/output device coordination.

5. Security – Authentication, access control.

6. Networking – Communication between systems.

7. Error Handling – Detecting and handling system errors.

5. OS Components

1. Kernel – Core part of OS, controls everything.

2. System Calls – Interface for programs to request OS services.

3. Shell – Command interpreter (CLI/GUI).

4. File System – Manages data storage.

6. GATE Important Points

• OS acts as a resource manager.

• Kernel is always loaded in memory.

• System calls = bridge between user programs and OS functions.

7. GATE 1-Mark Sample Question

Q: Which of the following is not a function of an operating system?
a) Process scheduling
b) Memory management
c) Compiling a program
d) File management

✅ Answer: c) Compiling a program

8. Quick Revision Mnemonic

“RPFMISEN” →
Resource Management, Process Management, File Management, Memory Management, I/O Management, Security, Error Handling, Networking.

Practice Questions (OS Basics)

Q1. Define Operating System in one line.

Answer: An OS is system software that acts as an interface between the user and computer hardware, managing resources and providing services.

Q2. Which OS type is used in air traffic control systems?

Answer: Real-Time Operating System (RTOS).

Q3. Which OS type is used for parallel execution on multiple CPUs?

Answer: Multiprocessing OS.

Q4. What is the main function of the Kernel?

Answer: The kernel manages hardware resources like CPU, memory, and I/O devices.

Q5. Which OS scheduling method gives each process equal CPU time?

Answer: Round Robin Scheduling.

Q6. Which OS is commonly used in mobile phones?

Answer: Android (Linux-based OS) and iOS.

Q7. What is a system call?

Answer: A system call is a way for user programs to request services from the OS kernel.

Q8. In a batch OS, can the user interact with the system while a job is running?

Answer: No, interaction is not possible until the batch job completes.

Q9. Which OS component interprets user commands?

Answer: Shell.

Q10. Name two functions of OS related to memory.

Answer: Allocation and deallocation of memory.

Day 1 – GATE Quick Recap Table