Operating System and Services in O.S.

📘 Operating System (OS)

Definition: An Operating System (OS) is system software that acts as an interface between the user and the computer hardware. It manages hardware resources, provides a user interface, and ensures that software applications run efficiently.

🛠️ Functions of an Operating System

1. Process Management: Handles creation, scheduling, and termination of processes.

2. Memory Management: Allocates and deallocates memory space as needed by programs.

3. File System Management: Organizes, stores, retrieves, and manages data in files and folders.

4. Device Management: Controls and manages input/output devices like keyboard, mouse, printers, etc.

5. Security and Access Control: Protects system data and resources from unauthorized access.

6. User Interface: Provides a way for users to interact with the system (CLI or GUI).

7. Networking: Allows computers to communicate over a network.

8. Error Detection and Handling: Detects and responds to errors in hardware and software.

⚙️ Services Provided by the Operating System

Service	Description
Program Execution	Loads and runs programs and provides runtime environment.
I/O Operations	Handles input and output operations from devices.
File System Access	Manages file creation, deletion, reading, and writing.
Communication	Enables data exchange between processes (inter-process communication).
Resource Allocation	Distributes resources like CPU time, memory, and I/O fairly among processes.
Error Handling	Detects and manages hardware/software errors smoothly.
Security and Protection	Ensures only authorized users/processes access data and system resources.

📌 Example Operating Systems

Examples: Windows, Linux, macOS, Android, iOS

📘 DOS – Disk Operating System

📜 History of DOS

Introduction: DOS (Disk Operating System) was one of the earliest operating systems for IBM-compatible personal computers. It was first developed by Microsoft in 1981 as MS-DOS (Microsoft Disk Operating System).

Key Fact: MS-DOS was based on an earlier OS called 86-DOS, which Microsoft acquired from Seattle Computer Products.

Use: DOS was a command-line-based OS used before Windows and was widely used throughout the 1980s and early 1990s.

📁 Files and Directories in DOS

Files: Files are units of data storage. In DOS, filenames followed the 8.3 format (up to 8 characters for name, 3 for extension).

Directories: Directories are used to organize files. The top-level directory is the root (`C:\`) and subdirectories can be created within it.

Commands: DOS allows users to create, navigate, and manage directories using commands like DIR, CD, MD, and DEL.

⚙️ Internal and External Commands

Internal Commands: These are built into the command interpreter (COMMAND.COM) and do not require separate files. Examples:

DIR – List files and directories
CLS – Clear the screen
COPY – Copy files
DEL – Delete files

External Commands: These are separate files stored on disk and loaded when needed. Examples:

FORMAT – Format a disk
DISKCOPY – Copy the contents of one disk to another
CHKDSK – Check disk for errors
XCOPY – Extended copy command for directories and files

📄 Batch Files

Definition: A batch file is a plain text file that contains a sequence of DOS commands. Its extension is .BAT.

Purpose: Used to automate repetitive tasks such as backups, starting programs, or setting configurations.

Example:

@echo off
echo Hello, this is a batch file.
pause

🖥️ Types of Operating Systems

1. Batch Operating System: Executes batches of jobs without user interaction. E.g., old mainframes.

2. Time-Sharing OS: Allows multiple users to access the system simultaneously. E.g., UNIX.

3. Distributed OS: Manages a group of independent computers and makes them appear as a single system.

4. Real-Time OS: Used in embedded systems, robotics, etc., where response time is critical. E.g., RTOS, VxWorks.

5. Network OS: Provides services to computers connected over a network. E.g., Windows Server, Novell NetWare.

6. Mobile OS: Designed for smartphones and tablets. E.g., Android, iOS.