Unix is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs. Today's Unix systems are split into various branches, developed over time by AT&T as well as various commercial vendors and non-profit organizations. Unix was designed to be portable, multi-tasking and multi-user in a time-sharing configuration. Unix systems are characterized by various concepts: the use of plain text for storing data; a hierarchical file system; treating devices and certain types of inter-process communication (IPC) as files. Under Unix, the "operating system" consists of many of these utilities along with the master control program, the kernel. The kernel provides services to start and stop programs, handles the file system and other common "low level" tasks that most programs share, and, perhaps most importantly, schedules access to hardware to avoid conflicts if two programs try to access the same resource or device simultaneously. To mediate such access, the kernel was given special rights on the system, leading to the division between user-space and kernel-space.
Components: The Unix system is composed of several components that are normally packed together. By including – in addition to the kernel of an operating system – the development environment, libraries, documents, and the portable, modifiable source-code for all of these components, Unix was a self-contained software system. This was one of the key reasons it emerged as an important teaching and learning tool and has had such a broad influence. The inclusion of these components did not make the system large – the original V7 UNIX distribution, consisting of copies of all of the compiled binaries plus all of the source code and documentation occupied less than 10MB, and arrived on a single 9-track magnetic tape. The printed documentation, typeset from the on-line sources, was contained in two volumes.
Flavors of UNIX :
The widely used term flavors of UNIX refers to the many Unix-like operating systems that have been developed based on the original UNIX that was written in 1969 by Ken Thompson at Bell Labs.
Fragmentation of UNIX occurred almost from the beginning. It was the result of both commercial pressures and differences in opinion among developers as to the way in which operating systems should behave.
Among the ways in which the various flavors of UNIX differ are (1) fundamental design, (2) commands and features, (3) the hardware platform(s) (i.e., processors) for which they are intended and (4) whether they are proprietary software (i.e., commercial software) or free software (i.e., software that anyone can obtain at no cost and use for any desired purpose).
Many of the proprietary flavors have been designed to run only (or mainly) on proprietary hardware sold by the same company that has developed them. Examples include:
Others are developed by groups of volunteers who make them available for free. Among them are:
Components: The Unix system is composed of several components that are normally packed together. By including – in addition to the kernel of an operating system – the development environment, libraries, documents, and the portable, modifiable source-code for all of these components, Unix was a self-contained software system. This was one of the key reasons it emerged as an important teaching and learning tool and has had such a broad influence. The inclusion of these components did not make the system large – the original V7 UNIX distribution, consisting of copies of all of the compiled binaries plus all of the source code and documentation occupied less than 10MB, and arrived on a single 9-track magnetic tape. The printed documentation, typeset from the on-line sources, was contained in two volumes.
Flavors of UNIX :
The widely used term flavors of UNIX refers to the many Unix-like operating systems that have been developed based on the original UNIX that was written in 1969 by Ken Thompson at Bell Labs.
Fragmentation of UNIX occurred almost from the beginning. It was the result of both commercial pressures and differences in opinion among developers as to the way in which operating systems should behave.
Among the ways in which the various flavors of UNIX differ are (1) fundamental design, (2) commands and features, (3) the hardware platform(s) (i.e., processors) for which they are intended and (4) whether they are proprietary software (i.e., commercial software) or free software (i.e., software that anyone can obtain at no cost and use for any desired purpose).
Many of the proprietary flavors have been designed to run only (or mainly) on proprietary hardware sold by the same company that has developed them. Examples include:
- AIX - developed by IBM for use on its mainframe computers
- BSD/OS - a commercial version of BSD developed by Wind River for Intel processors
- HP-UX - developed by Hewlett-Packard for its HP 9000 series of business servers
- IRIX - developed by SGI for applications that use 3-D visualization and virtual reality
- QNX - a real time operating system developed by QNX Software Systems primarily for use in embedded systems
- Solaris - developed by Sun Microsystems for the SPARC platform and the most widely used proprietary flavor for web servers
- Tru64 - developed by Compaq for the Alpha processor
Others are developed by groups of volunteers who make them available for free. Among them are:
- Linux - the most popular and fastest growing of all the Unix-like operating systems
- FreeBSD - the most popular of the BSD systems (all of which are direct descendants of BSD UNIX, which was developed at the University of California at Berkeley)
- NetBSD - features the ability to run on more than 50 platforms, ranging from acorn26 to x68k
- OpenBSD - may have already attained its goal of becoming the most secure of all computer operating systems
- Darwin - the new version of BSD that serves as the core for the Mac OS X
Today, there are three manufacturers that really dominate UNIX: IBM® (AIX) , Sun (Solaris) , and HP (HP-UX)
AIX
AIX (Advanced Interactive eXecutive) is IBM's homegrown UNIX operating system. AIX was first introduced by IBM in 1986. IBM ported AIX to its RS/6000® platform in 1989. The release of AIX Version 3 coincided with the announcement of the first RS/6000 models. The unique factor of these systems were that they outperformed all other machines in integer-compute performance and also by a factor of 10 in floating-point performance.
Version 4 was introduced in 1994 and added support for symmetric multiprocessing (SMP) with the first RS/6000 SMP servers. The operating system continued to evolve until 1999, when AIX 4.3.3 introduced workload management (WLM). In May 2001, IBM unveiled AIX 5L, the L standing for "Linux affinity", which coincided with the release of its POWER4™ servers, which provided for the logical partitioning of servers. IBM created their first midrange hypervisor around this combination. More than any other factor, this was the breakthrough that IBM needed to challenge HP and SUN for UNIX supremacy. In just a few short years, IBM would dominate the market. In October of 2002, IBM announced dynamic logical partitioning (DLPAR) with AIX 5.2. AIX 5.3, introduced in August 2004, provided many new features: virtualization, security, reliability, systems management, and administration. Most importantly , AIX 5.3 fully supported the Advanced Power Virtualization (APV) capabilities of the POWER architecture; this included micropartioning, virtual I/O servers, and symmetric multithreading (SMT).
SunOS version 1.0 was first introduced in 1983, along with support for Sun-1 and Sun-2 systems. SunOS Version 2.0, introduced in 1985, came out with the virtual file system (VFS) and NFS. In 1987, AT&T and Sun first announced that they would work together to help merge System V and BSD into one release, based on System V, release 4. SunOS was originally developed from the BSD flavor of UNIX in 1983. It was later rebranded as Solaris (starting with version 5), based on AT&T System V release IV, in 1993. The first 64-bit version of Sparc Solaris 7 would add support for file system metadata logging. Solaris 9, introduced in 2002, added support for Solaris Volume Manager and Linux capabilities. Their most important release would be Solaris 10, which was first introduced in 2005 and included many new features such as support for its new ZFS file system, Solaris Containers, and Logical Domains.
Version 1 of HP's UNIX (HP-UX) was first released in 1984. It was originally based on System V, release 3, and it ran exclusively on their RISC - PA-RISC HP 9000 platform. Version 9 introduced its character-based graphical user interface (GUI), SAM, which allowed you to administrator the system without using the command line. Version 10 was introduced in 1995, which brought changes in the layout of the system file and directory structure, making it strikingly similar in many ways to AT&T SVR4. Version 11 was first introduced in 1997. This was HP's first release to support 64-bit addressing. In 2000, 11i came to be, which introduced operating environments, defined as bundled groups of layered applications for specific IT purposes. In 2001, Version 11.20 introduced support for Itanium systems. Interestingly enough, HP-UX was the first UNIX that used Access Control Lists (ACLs) for file permissions. It was also one of the first to introduce built-in support for Logical Volume Manager.
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