System V Release 4.0 was announced on October 18, 1988 and was incorporated into a variety of commercial Unix products from early 1989 onwards.
 A joint project of AT&T Unix System Laboratories and Sun Microsystems, it combined technology from:
SVR3
4.3BSD
Xenix
SunOS
New features included:
From BSD: TCP/IP support, sockets, UFS, support for multiple groups, C shell.

From SunOS: the virtual file system interface (replacing the File System Switch in System V release 3), NFS, new virtual memory system including support for memory mapped files, an improved shared library system based on the SunOS 4.x model, the OpenWindows GUI environment, External Data Representation (XDR) and ONC RPC.

From Xenix: x86 device drivers, binary compatibility with Xenix (in the x86 version of System V).

Korn shell.

ANSI X3J11 C compatibility.

Multi-National Language Support (MNLS).

Better internationalization support.

An application binary interface (ABI) based on Executable and Linkable Format (ELF).

Support for standards such as POSIX and X/Open.

Many companies licensed SVR4 and bundled it with computer systems such as workstations and network servers.
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.

Software porting houses also sold enhanced and supported Intel x86 versions.
SVR4 software vendors included Dell (Dell UNIX), Everex (ESIX), Micro Station Technology (SVR4), Microport (SVR4), and UHC (SVR4).

The primary platforms for SVR4 were Intel x86 and SPARC; the SPARC version, called Solaris 2 (or, internally, SunOS 5.x), was developed by Sun.
The relationship between Sun and AT&T was terminated after the release of SVR4, meaning that later versions of Solaris did not inherit features of later SVR4.x releases.
Sun would in 2005 release most of the source code for Solaris 10 (SunOS 5.10) as the open-source OpenSolaris project, creating, with its forks, the only open-source (albeit heavily modified) System V implementation available.
After Oracle took over Sun, Solaris was forked into proprietary release, but illumos as the continuation project is being developed in open-source.

A consortium of Intel-based resellers including Unisys, ICL, NCR Corporation, and Olivetti developed SVR4.0MP with multiprocessing capability (allowing system calls to be processed from any processor, but interrupt servicing only from a "master" processor).

Release 4.1 ES (Enhanced Security) added security features required for Orange Book B2 compliance and Access Control Lists and support for dynamic loading of kernel modules.
System V Release 4.0 was announced on October 18, 1988 and was incorporated into a variety of commercial Unix products from early 1989 onwards.  A joint project of AT&T Unix System Laboratories and Sun Microsystems, it combined technology from:
SVR3
4.3BSD
Xenix
SunOS
New features included:
From BSD: TCP/IP support, sockets, UFS, support for multiple groups, C shell.
From SunOS: the virtual file system interface (replacing the File System Switch in System V release 3), NFS, new virtual memory system including support for memory mapped files, an improved shared library system based on the SunOS 4.x model, the OpenWindows GUI environment, External Data Representation (XDR) and ONC RPC.
From Xenix: x86 device drivers, binary compatibility with Xenix (in the x86 version of System V).
Korn shell.
ANSI X3J11 C compatibility.
Multi-National Language Support (MNLS).
Better internationalization support.
An application binary interface (ABI) based on Executable and Linkable Format (ELF).
Support for standards such as POSIX and X/Open.
Many companies licensed SVR4 and bundled it with computer systems such as workstations and network servers. 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.
Software porting houses also sold enhanced and supported Intel x86 versions. SVR4 software vendors included Dell (Dell UNIX), Everex (ESIX), Micro Station Technology (SVR4), Microport (SVR4), and UHC (SVR4).
The primary platforms for SVR4 were Intel x86 and SPARC; the SPARC version, called Solaris 2 (or, internally, SunOS 5.x), was developed by Sun. The relationship between Sun and AT&T was terminated after the release of SVR4, meaning that later versions of Solaris did not inherit features of later SVR4.x releases. Sun would in 2005 release most of the source code for Solaris 10 (SunOS 5.10) as the open-source OpenSolaris project, creating, with its forks, the only open-source (albeit heavily modified) System V implementation available. After Oracle took over Sun, Solaris was forked into proprietary release, but illumos as the continuation project is being developed in open-source.
A consortium of Intel-based resellers including Unisys, ICL, NCR Corporation, and Olivetti developed SVR4.0MP with multiprocessing capability (allowing system calls to be processed from any processor, but interrupt servicing only from a "master" processor).
Release 4.1 ES (Enhanced Security) added security features required for Orange Book B2 compliance and Access Control Lists and support for dynamic loading of kernel modules.
UNIX System V