Unix (Thompson and Ritchie 1974, 1978) is a general purpose operating system. It was developed by Ken Thompson and Dennis Ritchie on the PDP-11 minicomputers at Bell Labs in the early 70s. In 1975, Bell Labs released Unix to the general public. Initial recipients of this Unix system were mostly universities and non-profit institutions. It was known as the V6 Unix. This early version of Unix, together with the classic book on the C programming language (Kernighan and Ritchie 1988) started the Unix revolution on Operating Systems, with long-lasting effects even to this day.
1. AT&T Unix
Development of Unix at AT&T continued throughout the 1980s, cumulating in the release of the AT&T System V Unix (Unix System V 2017), which has been the representative Unix of AT&T.
System V Unix was a uniprocessor (single CPU) system. It was extended to multiprocessor versions in the late 80s (Bach 1986).
2. Berkeley Unix
Berkeley Unix (Leffler et al. 1989, 1996) refers to a set of variants of the Unix operating system developed by the Berkeley Software Distribution (BSD) at the University of California, Berkeley, from 1977 to 1985. The most significant contributions of BSD Unix are implementation of the TCP/IP suite and the socket interface, which are incorporated into almost all other operating systems as a standard means of networking, which has helped the tremendous growth of the Internet in the 90s. In addition, BSD Unix advocates open source from the beginning, which stimulated further porting and development of BSD Unix. Later releases of BSD Unix provided a basis for several open source development projects, which include FreeBSD (McKusick et al. 2004), OpenBSD and NetBSD, etc. that are still ongoing to this day.
3. HP Unix
HP-UX (HP-UX 2017) is Hewlett Packard’s proprietary implementation of the Unix operating system, first released in 1984. Recent versions of HP-UX support the HP 9000 series computer systems, based on the PA-RISC processor architecture, and HP Integrity systems, based on Intel’s Itanium. The unique features of HP-UX include a built-in logical volume manager for large file systems and access control lists as an alternative to the standard rwx file permissions of Unix.
4. IBM Unix
AIX (IBM AIX 2017) is a series of proprietary Unix operating systems developed by IBM for several of its computer platforms. Originally released for the IBM 6150 RISC workstation, AIX now supports or has supported a wide variety of hardware platforms, including the IBM RS/6000 series and later POWER and PowerPC-based systems, IBM System I, System/370 mainframes, PS/2 personal computers, and the Apple Network Server. AIX is based on UNIX System V with BSD4.3-compatible extensions.
5. Sun Unix
Solaris (Solaris 2017) is a Unix operating system originally developed by Sun Microsystems (Sun OS 2017). Since January 2010, it was renamed Oracle Solaris. Solaris is known for its scalability, especially on SPARC systems. Solaris supports SPARC-based and x86-based workstations and servers from Oracle and other vendors.
As can be seen, most Unix systems are proprietary and tied to specific hardware platforms. An average person may not have access to these systems. This present a challenge to readers who wishes to practice systems programming in the Unix environment. For this reason, we shall use Linux as the platform for programming exercises and practice.
Source: Wang K.C. (2018), Systems Programming in Unix/Linux, Springer; 1st ed. 2018 edition.