Operating System — the core system software that creates a connection between a computer’s hardware components and user applications, manages system resources, ensures the execution of programs, and provides the user with an interface to interact with the computer. The OS acts as the “control center” or “brain” of the computer and is absolutely essential for the system to function. Without an operating system, a computer is simply a non-functional collection of hardware.

What is an Operating System?

An Operating System is a complex software that loads as soon as the computer is powered on and provides the foundational platform for all other programs to run. The OS manages hardware, provides services to applications, and offers a user-friendly interface.

Simply put, the operating system is the program that tells the computer “what to do” and “how to do it.”

When you open a file, launch a program, connect to the internet, or use a printer — the OS is working behind the scenes.

Main Functions of an OS:

• Management of hardware resources (CPU, RAM, disk, network)
• Providing an execution environment for programs
• File and directory organization (file system)
• User interface (GUI or CLI)
• Security and access control
• Management of network connections
• Error handling and troubleshooting

Modern operating systems are multifunctional and consist of millions of lines of code. Windows has ~50 million lines, and the Linux kernel has ~30 million. Building these systems requires decades of work by thousands of engineers.

History of Operating Systems

Early era (1950s):

Early computers ran without operating systems. Programmers interacted directly with hardware, and each program contained its own I/O routines. Late 1950s introduced simple batch processing systems — tasks were processed sequentially using punch cards or tapes.

Batch and Time-sharing systems (1960s):

In the 1960s, advanced OS/360 was created for IBM mainframes. Batch processing improved, and the concept of time-sharing appeared — multiple users could “share” the computer simultaneously. Systems like Multics (1965) and CTSS were developed.

The Unix Revolution (1969–1970):

In 1969, Ken Thompson and Dennis Ritchie created Unix at AT&T Bell Labs. Unix was revolutionary due to its simplicity, power, portability, and modular design. In 1972, it was rewritten in C, enabling it to run on various platforms.

Unix philosophy: “Do one thing and do it well.”

Personal Computer OS (1970–1980s):

With the rise of microcomputers, simple OSes appeared. CP/M (1974) became the first widely used microcomputer OS.

In 1981, the IBM PC introduced MS-DOS, a command-line OS that became massively popular and marked the rise of Microsoft.

Apple released Apple II (1977, Apple DOS) and Macintosh (1984, Mac OS), which featured the first mass-market GUI — windows, icons, menus, mouse (WIMP interface).

GUI Revolution and Windows (1980–1990s):

Xerox PARC created the GUI concept; Apple commercialized it; Microsoft popularized it.

Windows 1.0 (1985) was a graphical shell for MS-DOS.

Windows 3.0/3.1 became successful.

Windows 95 was revolutionary — Start Menu, Taskbar, 32-bit, Plug and Play, long filenames.

Then came Windows 98, ME, 2000, XP (2001—most popular), Vista, 7 (2009), 8, 10 (2015), 11 (2021).

Linux and Open Source (1991–present):

In 1991, Linus Torvalds created a Unix-like kernel (Linux). Combined with GNU tools, GNU/Linux was formed.

Popular distributions: Debian, Red Hat, Ubuntu, Fedora, Arch, Mint.

Linux dominates servers (~90%), supercomputers (100%), Android, and embedded systems.

Mobile OS era (2000–2010s):

iOS (2007) and Android (2008) transformed mobile computing.

Today: Android ~70%, iOS ~27%.

Modern era (2010–present):

Cloud computing, containerization (Docker, Kubernetes), ChromeOS, HarmonyOS, real-time OS, IoT OS.

Windows 11, macOS on Apple Silicon (M1–M4).

Main Components of an Operating System

1. Kernel

The kernel is the core of the OS. It runs in privileged mode and interacts directly with hardware.

Kernel types:

• Monolithic kernel: Everything runs in kernel space (Linux, Unix)
• Microkernel: Minimal features in kernel, rest in user space (Minix, QNX)
• Hybrid kernel: Mix of both (Windows NT, macOS)
• Exokernel: Minimal abstraction, experimental

2. Process and Thread Management

• Process: Instance of a running program
• Thread: Execution unit within a process

Scheduling algorithms: FCFS, SJF, Round Robin, Priority, Multilevel Queue.

Context switching: switching between processes/threads.

Multitasking, multiprocessing, SMP.

3. Memory Management

• Physical and virtual memory
• Paging, page tables
• Swap space / pagefile
• Stack and heap
• Memory protection
• Garbage collection (Java, Python, C#)

4. File System

File systems organize data storage on disks.

Examples:

Windows: NTFS, FAT32, exFAT, ReFS

macOS: APFS, HFS+

Linux: ext4, Btrfs, XFS, ZFS

Functions: create/read/write/delete files, metadata, permissions, journaling.

Directory structure:

• Windows: C:, D:\
• Linux/Unix: /

5. Device and I/O Management

Device drivers, I/O scheduling, buffering/caching, interrupts, DMA.

6. User Interface

GUI (Windows, macOS, GNOME, KDE) and CLI (cmd, PowerShell, Bash, Zsh).

7. Network Management

TCP/IP stack, DNS, DHCP, firewall, VPN, sockets.

8. Security

User authentication, access control, admin/root privileges, encryption (BitLocker, FileVault, LUKS), security updates, sandboxing, SELinux/AppArmor.

Comparison of Operating Systems

Windows

• Wide hardware support, games, large software base
• – Paid license, malware target, privacy concerns

macOS

• Stable, secure, Unix-based, strong Apple ecosystem
• – Only Apple hardware, expensive, weaker gaming support

Linux

• Free, open-source, stable, customizable, privacy-friendly
• – Steeper learning curve, limited desktop app support

Android

• Open source, customizable, huge device variety
• – Fragmentation, malware risk

iOS

• Secure, polished, high-quality apps, long updates
• – Closed system, expensive, limited customization

Future of Operating Systems

• Cloud & hybrid OS
• Deep AI integration
• Containers & virtualization
• Real-time and edge OS
• Security-centric design
• Unified multi-device OS
• Possible microkernel comeback

In conclusion, an operating system is the heart and soul of any computer system. No matter how powerful the hardware is, it becomes useless without an OS to control it. Windows, macOS, Linux, Android, and iOS — each has its own philosophy, strengths, and role.

The future will bring smarter, more secure, cloud-integrated, AI-powered operating systems.