UNIXes

Unixes are a collective term for operating systems that derive from the original AT&T Unix or that implement a Unix-compatible API and behavior. In practice, "Unix" can refer to systems that meet The Open Group's Single UNIX Specification and bear the UNIX trademark, or to Unix-like systems that imitate Unix interfaces without holding certification. The Unix lineage began at Bell Labs in 1969, with the development of early releases that led to Version 7 and the ensuing BSD variants. Over time Unix evolved into several major branches, including System V from AT&T, BSD from University of California variants, and a family of commercial derivatives.

The standards landscape is shaped by POSIX (IEEE Std 1003.x) and the Open Group's Single UNIX Specification, which define a common API, behavior, and command set expected of certified systems. Certification is voluntary and grants the right to use the UNIX trademark.

Examples of certified Unix systems today include Oracle Solaris, IBM AIX, and Hewlett-Packard's HP-UX; macOS is certified as UNIX 03 under the specification. The BSD family—FreeBSD, NetBSD, and OpenBSD—are Unix-like and not themselves UNIX-certified, but they closely follow Unix design principles. Linux, though not certified as UNIX, is the most widely used Unix-like kernel and, with user-space tools from the GNU project and others, provides a compatible environment on many distributions.

Unixes share core concepts such as a hierarchical file system, process management, and a standard toolset, but they differ in implementation, performance, and hardware support. They remain influential in enterprise, academic, and embedded computing.