Evolution of Operating Systems: Generations & Concepts

Historical Operating Systems: A Timeline

This document provides a brief history of operating systems, covering their evolution across different generations.

1st Generation (1945-1955)

Characterized by vacuum valves and machine language. These systems were large, consumed high energy, were very slow, and performed simple mathematical calculations.

2nd Generation (1955-1965)

Transitioned to transistors and batch processing. Systems became smaller and consumed less power.

3rd Generation (1965-1980)

Integrated circuits were introduced, making systems cheaper and enabling multiple processors to run concurrently.

4th Generation (1980-Present)

Marked by the advent of personal computers.

Memory Management

The memory manager is a crucial part of the OS. It is responsible for:

• Keeping track of memory parts in use and those available.
• Managing data exchange between memory and the fixed disk.

Fixed Disk Partitions

Memory is partitioned into several pieces. Each piece is called a partition. Partitions are created during machine boot and cannot be resized, hence the term "fixed partitions."

Variable Partitions

Variable partitions were implemented to address the limitations of fixed partitions. They are created and destroyed based on system load variations.

Processing

Key features of processing include:

• A process must reside entirely in memory and have all necessary resources allocated to begin execution.
• Each process is protected from other processes and cannot write to memory areas belonging to other processes.

There are two main modes:

• User Mode: The user operates in this mode.
• Kernel or Privileged Mode: This mode belongs to the OS.

Process Control Block (PCB)

The PCB contains vital information about a process, including:

• Process Identifier (PID)
• Process Status (ready, waiting, locked)
• Priority
• Owner
• Synchronization: Processes can communicate and collaborate.

System Components

• User: Controls the user level, showing the user the processes running or to be executed.
• Supervisor: Responsible for communication between the system and the user for each process. Manages and coordinates input/output for different processes to peripherals and external storage devices.
• Board: Manages memory and puts processes into memory for execution.
• Nucleus: The CPU handles control and manages the processes that appear on the computer for execution.