As of 2021[update], the AT&T-derived Unix market is divided between four System V variants: IBM's AIX, Hewlett Packard Enterprise's HP-UX and Oracle's Solaris,[2] plus the free-software illumos forked from OpenSolaris.

A standards document called the System V Interface Definition outlined the default features and behavior of implementations.

The divide was roughly between longhairs and shorthairs; programmers and technical people tended to line up with Berkeley and BSD, more business-oriented types with AT&T and System V.While HP, IBM and others chose System V as the basis for their Unix offerings, other vendors such as Sun Microsystems and DEC extended BSD.

Since the early 1990s, due to standardization efforts such as POSIX and the success of Linux, the division between System V and BSD has become less important.

System V also included features such as the vi editor and curses from 4.1 BSD, developed at the University of California, Berkeley; it also improved performance by adding buffer and inode caches.

It also added support for inter-process communication using messages, semaphores, and shared memory, developed earlier for the Bell-internal CB UNIX.

User interface improvements included the "layers" windowing system for the DMD 5620 graphics terminal, and the SVR3.2 curses libraries that offered eight or more color pairs and other at this time important features (forms, panels, menus, etc.).

Among the more obscure distributions of SVR3.2 for the 386 were ESIX 3.2 by Everex and "System V, Release 3.2" sold by Intel themselves; these two shipped "plain vanilla" AT&T's codebase.

System V Release 4.0 was announced on October 18, 1988[15] and was incorporated into a variety of commercial Unix products from early 1989 onwards.

SVR4 systems vendors included Atari (Atari System V), Commodore (Amiga Unix), Data General (DG/UX), Fujitsu (UXP/DS), Hitachi (HI-UX), Hewlett-Packard (HP-UX), NCR (Unix/NS), NEC (EWS-UX, UP-UX, UX/4800, SUPER-UX), OKI (OKI System V), Pyramid Technology (DC/OSx), SGI (IRIX), Siemens (SINIX), Sony (NEWS-OS), Sumitomo Electric Industries (SEIUX), and Sun Microsystems (Solaris) with illumos in the 2010s as the only open-source platform.

After Oracle took over Sun, Solaris was forked into proprietary release, but illumos as the continuation project is being developed in open-source.

[25] SCO also introduced Smallfoot in 2004, a low-resource "embeddable" variant of UnixWare for dedicated commercial and industrial applications, in an attempt that was perceived as a response to the growing popularity of Linux.

In late 1994, Eric S. Raymond discontinued his PC-clone UNIX Software Buyer's Guide on USENET, stating, "The reason I am dropping this is that I run Linux now, and I no longer find the SVr4 market interesting or significant.

Once Linux proved itself by executing the most complex calculations possible, IT managers quickly grasped that it could easily serve Web pages and run payroll.

Naturally, it helps to be lucky: Free, downloadable Linux's star began to rise during one of the longest downturns in IT history.

With companies doing more with less, one thing they could dump was Unix.The article also cites trends in high-performance computing applications as evidence of a dramatic shift from Unix to Linux:[31] A look at the Top500 list of supercomputers tells the tale best.

The principal variants of System V that remain in commercial use are AIX (IBM), Solaris (Oracle), and HP-UX (HP).

[2] Industry analysts generally characterize proprietary Unix as having entered a period of slow but permanent decline.

[36] Modern System V, Linux, and BSD platforms use the ELF file format for natively compiled binaries.