Operating System

macOS Unix-based operating system developed by Apple

Linux A free, open-source, Unix-like operating system

Windows A family of graphical operating systems developed by Microsoft

What is a Operating System?

An operating system (OS) is the core software that manages a computer’s hardware and software resources, acting as a bridge between users/applications and the physical components of the system. It’s the “conductor” of your device—orchestrating everything from memory allocation to running apps.

Core Functions of an OS

Function	Description
Hardware Management	Controls CPU, RAM, storage, peripherals (printers, keyboards), and network devices via drivers.
Process Management	Creates, schedules, and terminates processes (apps). Balances CPU time via multitasking.
Memory Management	Allocates RAM to apps, uses virtual memory (disk space as RAM) when physical RAM is full.
File System Management	Organizes files/folders on storage (HDD/SSD). Manages permissions (e.g., NTFS, APFS, ext4).
User Interface (UI)	Provides interaction: GUI (graphical, e.g., Windows/macOS desktop) or CLI (command line, e.g., Terminal).
Security & Access Control	Enforces user authentication, file permissions, and firewall rules.
Networking	Manages network connections (Wi-Fi/Ethernet), protocols (TCP/IP), and data routing.

Key Components

Kernel
- The core of the OS. Directly interacts with hardware.
- Types:
  - Monolithic (Linux, UNIX): Kernel handles all tasks (fast but complex).
  - Microkernel (macOS, QNX): Minimalist kernel; delegates tasks to user-space services (stable but slower).
  - Hybrid (Windows NT): Mixes monolithic/microkernel approaches.
System Libraries
- Pre-written code (APIs) that apps use to request OS services (e.g., opening files).
Hardware Abstraction Layer (HAL)
- Isolates hardware-specific code, letting the OS run on different devices.
User Interface
- Shell: CLI interpreter (e.g., Bash, PowerShell).
- GUI: Visual desktop (icons, windows, menus).

Types of Operating Systems

Type	Use Case	Examples
Desktop/Server	PCs, workstations, servers	Windows, macOS, Linux (Ubuntu, Fedora).
Mobile	Smartphones, tablets	Android (Linux-based), iOS/iPadOS (Unix-based).
Embedded	IoT devices, appliances	FreeRTOS, Raspberry Pi OS.
Real-Time (RTOS)	Mission-critical systems	VxWorks, QNX (autonomous cars, aircraft).

How an OS Works: Simplified

Boot Process:
- BIOS/UEFI → Bootloader → Kernel → Drivers → User interface.
Running an App:
- You click a program → OS loads it into RAM → CPU executes instructions → OS handles input/output.
Multitasking:
- OS rapidly switches CPU between apps (e.g., browser + music player), creating the illusion of simultaneous operation.

OS vs. Software vs. Firmware

Component	Role	Example
OS	Manages hardware/software resources.	Windows 11, Ubuntu.
Software	Apps running on top of the OS.	Chrome, Photoshop.
Firmware	Low-level code embedded in hardware.	BIOS, UEFI, router firmware.

Why Operating Systems Matter

Hardware Utilization: Maximizes CPU/RAM efficiency.
Abstraction: Apps don’t need direct hardware access (simplifies development).
Security: Isolates apps to prevent crashes/malware spread.
Consistency: Provides standardized interfaces for developers.
User Productivity: Enables multitasking, file management, and networking.

Evolution Milestones

1980s: MS-DOS (CLI-driven), Macintosh System 1 (first consumer GUI).
1990s: Windows 95 (GUI revolution), Linux (open-source kernel).
2000s: macOS (Unix-based), Android/iOS (mobile dominance).
2020s: AI integration (e.g., Windows Copilot), cross-device sync (Apple Continuity).

Fun Fact

Early computers had no OS! Programs ran directly on hardware via punch cards. The first OS (GM-NAA I/O, 1956) was created for IBM mainframes to manage batch jobs.

In essence:

An OS is the ultimate multitasker—transforming raw hardware into a responsive, secure, and user-friendly tool. Whether you’re gaming on Windows, coding on Linux, or editing video on macOS, the OS is the invisible force making it all possible.