“Linux is a Unix clone written from scratch by Linus Torvalds with assistance from a loosely-knit team of hackers across the Net. It aims towards POSIX compliance.”

Source: http://www.cyberciti.biz/faq/what-is-the-difference-between-linux-and-unix/

This is what CDE Unix Desktop looked like in 1999: (RISC technology!)

“It gradually sank into obscurity as the x86 PC displaced RISC workstations and Linux replaced the various expensive flavours of Unix, but it never entirely went away.”

Source: http://www.theregister.co.uk/2012/08/09/cde_goes_opensource/

POSIX:

• POSIX.1: Core Services (incorporates Standard ANSI C) (IEEE Std 1003.1-1988)
  • Process Creation and Control
  • Signals
  • Floating Point Exceptions
  • Segmentation / Memory Violations
  • Illegal Instructions
  • Bus Errors
  • Timers
  • File and Directory Operations
  • Pipes
  • C Library (Standard C)
  • I/O Port Interface and Control
  • Process Triggers

• POSIX.1b: Real-time extensions (IEEE Std 1003.1b-1993, later appearing as librt—the Realtime Extensions library)^[8])
  • Priority Scheduling
  • Real-Time Signals
  • Clocks and Timers
  • Semaphores
  • Message Passing
  • Shared Memory
  • Asynchronous and Synchronous I/O
  • Memory Locking Interface

• POSIX.1c: Threads extensions (IEEE Std 1003.1c-1995)
  • Thread Creation, Control, and Cleanup
  • Thread Scheduling
  • Thread Synchronization
  • Signal Handling

• POSIX.2: Shell and Utilities (IEEE Std 1003.2-1992)
  • Command Interpreter
  • Utility Programs

Depending upon the degree of compliance with the standards, one can classify operating systems as fully or partly POSIX compatible. Certified products can be found at the IEEE’s website.^[16]

POSIX-certified

Some versions of the following operating systems have been certified to conform to one or more of the various POSIX standards. This means that they passed the automated conformance tests.^[17]

• AIX^[18]
• HP-UX^[19]
• IRIX^[20]
• OS X (since 10.5 Leopard)^{[21][22][discuss]}
• Solaris^[23]
• Tru64^[19]
• UnixWare^[24]
• QNX Neutrino^[25]
• Inspur K-UX^[26]
• Integrity^[27]

Mostly POSIX-compliant

The following, while not officially certified as POSIX compatible, comply in large part:

• Android (Available through Android NDK)^{[citation needed]}
• BeOS (and subsequently Haiku)
• Contiki
• Darwin (core of OS X and iOS)
• FreeBSD^[28]
• illumos
• Linux (most distributions — see Linux Standard Base)
• MINIX (now MINIX3)
• MPE/iX^[29]
• NetBSD
• Nucleus RTOS
• NuttX
• OpenBSD
• OpenSolaris^[30]
• PikeOS RTOS for embedded systems with optional PSE51 and PSE52 partitions; see partition (mainframe)
• RTEMS – POSIX API support designed to IEEE Std. 1003.13-2003 PSE52
• Sanos
• SkyOS
• Syllable
• VSTa
• VxWorks (VxWorks is often used as a shell around non-POSIX Kernels — i.e. TiMOS/SROS)
• Xenix

Source: https://en.wikipedia.org/wiki/POSIX

Related Links:

https://en.wikipedia.org/wiki/Single_UNIX_Specification

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