UNIX

Origins & Founders

• Developed in 1969 at AT&T’s Bell Labs.
• Key creators: Ken Thompson, Dennis Ritchie, and colleagues.
• Originally written in assembly language, later rewritten in C (1973), which made it portable across different hardware.

Historical Evolution

• 1969: First version of UNIX created for PDP‑7 minicomputer.
• 1970s: Spread to universities and research labs; became popular in academia.
• 1980s: Commercial variants emerged (e.g., SunOS, HP‑UX, AIX).
• 1990s: UNIX standards developed (POSIX, Single UNIX Specification).
• 2000s–present: Influenced modern OS design; macOS is certified UNIX, Linux is UNIX‑like.

Architecture

• Kernel:
  • Monolithic design, manages processes, memory, file systems, and devices.
• File System:
  • Hierarchical structure with root (/) directory.
  • “Everything is a file” philosophy (devices, processes, sockets).
• User Space:
  • Shells (sh, csh, ksh, bash) for command‑line interaction.
  • Utilities (grep, awk, sed, etc.).
• Security:
  • User/group permissions, access control, multi‑user environment.

Key Features

• Portability: Written in C, easily adapted to new hardware.
• Multi‑user & Multitasking: Supports multiple users and processes simultaneously.
• Networking: Strong TCP/IP support, widely used in servers.
• Stability & Reliability: Known for robustness in enterprise environments.
• Influence: Basis for POSIX standards, inspiration for Linux, BSD, and macOS.

Usage Scenarios

• Servers: Web hosting, databases, enterprise systems.
• Workstations: Scientific and engineering computing.
• Education: Teaching OS concepts and programming.
• Modern Descendants: macOS (certified UNIX), BSD variants (FreeBSD, OpenBSD), Solaris.