Introduction #

Operating systems did not appear fully formed.
They evolved step by step as computer usage changed.

Understanding this evolution helps you see why modern OS design looks the way it does.

Early Systems – No Operating System

In the beginning, there was no operating system.

Programs were:

• Loaded manually
• Run one at a time
• Written specifically for the hardware

The programmer had to:

• Control the CPU directly
• Manage memory manually
• Handle input and output

This worked when systems were simple, but it did not scale.

Batch Operating Systems #

As computers became more expensive, efficiency became important.

Batch systems were introduced:

• Programs were collected in batches
• Executed one after another
• No user interaction during execution

This improved hardware usage, but systems were still slow and inflexible.

Multiprogramming Systems #

To improve CPU utilization, multiprogramming was introduced.

The idea was simple:

• Keep multiple programs in memory
• Switch the CPU when one program waits for I/O

This reduced idle CPU time and improved performance.

This stage laid the foundation for modern multitasking.

Time-Sharing Systems #

Time-sharing systems were developed to support interactive users.

In these systems:

• Many users shared the same computer
• Each user felt they had their own machine
• The OS switched tasks quickly

This is where multitasking and multi-user concepts became standard.

Personal Computer Operating Systems #

With the rise of personal computers:

• OS became user-friendly
• Graphical interfaces were introduced
• Systems were designed for individual users

Examples include early versions of Windows and Unix-based systems.

Networked and Distributed Systems #

As networking grew:

• Systems started communicating with each other
• Resources were shared over networks
• Remote access became common

Operating systems added:

• Networking stacks
• Remote login support
• Distributed resource management

Linux grew strongly during this phase.

Modern Operating Systems #

Modern operating systems combine all previous ideas:

• Multitasking
• Multi-user support
• Networking
• Security
• Virtual memory
• Device abstraction

They run on:

• Desktops
• Servers
• Embedded devices
• Cloud platforms

Linux is a good example of this evolution.

Summary #

Operating systems evolved because:

• Hardware changed
• Usage patterns changed
• Performance and reliability demands increased

Each stage solved problems from the previous one.

Understanding this evolution helps you appreciate why modern OS design includes concepts like scheduling, memory management, and process isolation.