Posix Standards

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

Before 1997

POSIX was made up of the following standards:

POSIX.1: Core Services (IEEE Std 1003.1-1988)

Incorporates ANSI C (aka C89, C90)
Process Creation/Control
Signals (floating point exceptions, segmentation/memory violations, illegal instructions, etc)
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 librtthe Realtime Extensions library)

Priority Scheduling
Real-Time Signals
Clocks and Timers
Semaphores
Message Passing
Shared Memory
Async/Sync IO
Memory Locking

POSIX.1c (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

After 1997

POSIX.1-2001 (IEEE Std 1003.1-2001 or "Single UNIX Specification version 3")
POSIX.1-2008 (IEEE Std 1003.1-2008, 2016 Edition)
POSIX.1-2017 (IEEE Std 1003.1-2017)