• Computers: Vacuum tube-based machines.

• Operation: Manual setup using switches and plugboards.

• Programs: Written in machine language.

• No OS – everything was hardcoded and run manually.

• Example: ENIAC, UNIVAC.

2nd Generation (Mid-1950s – Early 1960s): Batch Operating Systems

• Hardware: Transistors, punch cards.

• Main Feature: Batch processing – jobs were grouped together and executed without user interaction.

• Job control language (JCL) used to instruct the OS.

• Limitations: No interaction during execution.

• Example OS: IBM’s early batch systems.

3rd Generation (Mid-1960s – 1970s): Multiprogramming and Time-Sharing OS

• Main Features:

  • Multiprogramming: Run multiple jobs in memory at the same time.

  • Time-sharing: CPU time split among users to give interactive access.

  • Spooling: Manage I/O better (e.g., printing).

• Users could now interact with the computer directly.

• Examples: UNIX, IBM OS/360.

4th Generation (Late 1970s – 1990s): Personal Computer Operating Systems

• Key Development: Emergence of personal computers (PCs).

• OS with GUI (Graphical User Interface) became popular.

• More user-friendly, included multitasking and file management.

• Examples: MS-DOS, Windows 3.x, macOS (Classic), early Linux.

5th Generation (1990s – Present): Modern Operating Systems

• Key Features:

  • Multitasking and multi-threading

  • Security, networking, and multimedia support

  • Support for mobile, cloud, and distributed computing

  • Virtualization and cloud integration

• Examples: Windows 10/11, modern macOS, Linux (Ubuntu, Fedora), Android, iOS.

Current and Future Trends:

• Cloud OS – Run systems on virtual machines (e.g., Google Cloud OS).

• Mobile OS – Android, iOS dominate phones.

• Real-Time OS (RTOS) – Used in embedded and critical systems.

• AI-integrated systems, edge computing, and IoT-ready OSs are the future.