UNIX System V
Unix System V commonly abbreviated
SysV and rarely called System 5, was one of the versions of the
Unix operating system. It was originally developed by AT&T and first released in
1983. Four major versions of System V were released, termed Releases 1, 2, 3 and 4. System V Release 4, or SVR4, was the most successful version, and the source of several common Unix features, such as "SysV
init scripts" (
/etc/init.d), used to control system startup and shutdown. The system also forms the basis of the
System V Interface Definition (SVID), a standard defining how System V systems should work.
While AT&T sold their own hardware which ran System V (see
AT&T Computer Systems), most customers ran a version from a reseller, based on AT&T's
reference implementation. Popular SysV derivatives include Dell SVR4 and Bull SVR4. The most widely used versions of System V today are
IBM's
AIX and
SCO OpenServer, based on System V Release 3, and
Sun Microsystems'
Solaris Operating System and SCO
UnixWare, both based on System V Release 4.
System V was an enhancement over AT&T's first commercial Unix called
System III (System IV was an AT&T-internal version). Traditionally, System V has been considered one of the two major "flavors" of UNIX, the other being
BSD. However, with the advent of Unix implementations developed from neither code base, such as
Linux and
QNX, this generalisation is not as accurate as it once was, and in any case standardisation efforts such as
POSIX are tending to reduce the differences between implementations.
During the period of the
Unix wars System V was known for being the primary choice of manufacturers of large multiuser systems, in opposition to
BSD's dominance of desktop workstations.
The first version of System V (also called System V.0 or System V Release 1, SVR1) was released in 1983. Developed by AT&T's Unix System Development Labs (USDL), a merger of the Unix Support Group and the
PWB group, it was based on System III and the Bell Labs internal UNIX/TS 5.0. System V also included features such as the
vi editor and
curses from the
Berkeley Software Distribution of UNIX developed at the
University of California, Berkeley (UCB). System V ran on the DEC
VAX machine. It also added support for
inter-process communication using messages,
semaphores, and
shared memory.
System V Release 2 was released in 1984. It added
shell functions and the
SVID. The concept of the "porting base" was formalized, and the DEC VAX 11/780 was named for this Release. The "porting base" is the so-called original version of a Release, from which all porting efforts for other machines emanate.
Apple Computer's
A/UX operating system was based on this release, although it was heavily integrated with the
Macintosh Toolbox.
System V Release 3 was released in 1987. It included
STREAMS, the
Remote File System (RFS), a restricted form of
shared libraries, and the
Transport Layer Interface (TLI) network
API. The
AT&T 3B2 became the official "porting base".
IBM's
AIX operating system is an SVR3 derivative.SVR3 was also the first System V version to have demand paged virtual memory. At the time, the implementation was superior to the BSD 4.2 demand paging, mainly because it supported 4k pages, as opposed to BSD's 1024-byte pages.
System V Release 4.0 was announced on
November 1,
1989 and was released in
1990. A joint project of
Unix System Laboratories and
Sun Microsystems, it combined technology from Release 3 as well as
4.3BSD,
Xenix, and
SunOS:
*From BSD:
TCP/IP support, sockets,
csh*From SunOS: the
virtual file system interface (replacing the one in System V release 3, the "File System Switch"),
Network File System (NFS), new virtual memory system including support for
memory mapped files, an improved shared library system based on the SunOS 4.x model, the
OpenLook GUI environment
*From Xenix: x86
device drivers
*Other improvements:
**
ksh**
ANSI C compatibility
**better
internationalization support
**an
application binary interface (ABI)
**support for standards such as
POSIX,
X/Open, and SVID3
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 the only open-source (heavily modified) System V implementation available.
Many versions of SVR4 appeared, because of hardware vendors (,
SGI) adapting it to their platform, and because porting houses (SCO,
Microport, ESIX, UHC) sold enhanced and supported x86 versions. SVR4 was even ported to the
Amiga as
Amiga Unix.
SVR4.0MP
Built by a consortium of Intel based resellers (including
Unisys,
International Computers Ltd. and
NCR Corporation. It provided a limited multi-processor capability. This allowed operating system calls to be processed from any processor, but interrupt servicing only from a "master" processor.
SVR4.1
Release 4.1 added asynchronous I/O.
SVR4.2
Release 4.2, developed in
1992 added support for the
Veritas filesystem,
access control lists (ACLs), and dynamically loadable kernel
modules.
Again, several versions of SVR4.2 appeared, including
Univel (later SCO)
UnixWare 1, UHC UnixWare, and Consensys.
SVR4.2MP
Release 4.2MP, completed late
1993, added support for
multiprocessing. It was released as UnixWare 2.
Release 5 was released as SCO UnixWare 7 by
SCO. SCO's successor,
The SCO Group also based
SCO OpenServer 6 on SVR5, but the codebase is not used by any other manufacturer.
*
PC-clone UNIX Software Buyer's Guide by
Eric S. Raymond (posted to
USENET in
1994)
*
Unix FAQ - history*
A Unix History Diagram - The original and continuously updated version of the Unix history, as published by
O'Reilly
