operating system

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operating system (OS)

Software that controls the operation of a computer, directs the input and output of data, keeps track of files, and controls the processing of computer programs. Its roles include managing the functioning of the computer hardware, running the applications programs, serving as an interface between the computer and the user, and allocating computer resources to various functions. When several jobs reside in the computer simultaneously and share resources (multitasking), the OS allocates fixed amounts of CPU time and memory in turn or allows one job to read data while another writes to a printer and still another performs computations. Through a process called time-sharing, a large computer can handle interaction with hundreds of users simultaneously, giving each the perception of being the sole user. Modern computer operating systems are becoming increasingly machine-independent, capable of running on any hardware platform; a widely used platform-independent operating system in use today on mainframe computers is UNIX. Most personal computers run on Microsoft's Windows operating system, which grew out of and eventually replaced MS-DOS. Seealso Linux.

Learn more about operating system (OS) with a free trial on Britannica.com.

Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

IBM AIX (operating system)

AIX (Advanced Interactive eXecutive) is the name given to a series of proprietary operating systems sold by IBM for several of its computer system platforms, based on UNIX System V with 4.3BSD-compatible command and programming interface extensions.

AIX runs on up to 64 IBM POWER or PowerPC architecture central processing units and two terabytes (TB) of random access memory. The JFS2 file system—first introduced by IBM as part of AIX—allows computer files and partitions over 16 TB in size.

History

AIX Version 1, introduced in 1986 for the IBM 6150 RT workstation, was based on UNIX System V Releases 1 and 2. In developing AIX, IBM and INTERACTIVE Systems Corporation (whom IBM contracted) also incorporated source code from 4.2 and 4.3BSD UNIX.

Among other variants, IBM later produced AIX Version 3 (also known as AIX/6000), based on System V Release 3, for their IBM POWER-based RS/6000 platform. Since 1990, AIX has served as the primary operating system for the RS/6000 series (later renamed IBM eServer pSeries, then IBM System p, and now IBM Power Systems). AIX Version 4, introduced in 1994, added symmetric multiprocessing with the introduction of the first RS/6000 SMP servers and continued to evolve though the 1990s, culminating with AIX 4.3.3 in 1999. Version 4.1, in a slightly modified form, was also the standard operating system for the Apple Network Server systems sold by Apple Computer to complement the Macintosh line.

In the late 1990s, under Project Monterey, IBM and the Santa Cruz Operation planned to integrate AIX and UnixWare into a single 32-bit/64-bit multiplatform UNIX with particular emphasis on running on Intel IA-64 architecture CPUs. A beta test version of AIX 5L for IA-64 systems was released, but according to documents released in SCO vs. IBM, less than forty licenses for the finished Monterey Unix were ever sold before the project was terminated in 2002.

AIX 6 was announced in May of 2007 and ran an open beta from June 2007 until the general availability (GA) of AIX 6.1 on November 9th, 2007. Major new features in AIX 6.1 included full role-based access control, workload partitions (which enable application mobility), and live partition mobility on the POWER6 hardware.

SCO lawsuit

In the SCO v. IBM lawsuit filed in 2003, the SCO Group alleged that (among other infractions) IBM had misappropriated licensed source code from UNIX System V Release 4 for incorporation into AIX; SCO subsequently withdrew IBM's license to develop and distribute AIX. IBM maintains that their license was irrevocable, and continued to sell and support the product until the litigation was adjudicated.

On 2007-08-10 the U.S. district court ruled that SCO does not own the copyrights to the Unix operating system.

Supported hardware platforms

IBM 6150 RT

The original AIX (sometimes called AIX/RT) was developed for the IBM 6150 RT workstation by IBM in conjunction with INTERACTIVE Systems Corporation, who had previously ported UNIX System III to the IBM PC for IBM as PC/IX. Installation media consisted of eight 1.2M floppy disks. The RT was based on the ROMP chip, the first commercial RISC chip, based on a design, the IBM 801, pioneered at IBM Research.

One of the novel aspects of the RT design was the use of a microkernel, called Virtual Resource Manager (VRM). The keyboard, mouse, display, disk drives and network were all controlled by a microkernel One could "hotkey" from one operating system to the next using the Alt-Tab key combination. Each OS in turn would get possession of the keyboard, mouse and display. Besides AIX v2, the PICK OS also utilized this microkernel.

Much of the AIX v2 kernel was written in the PL/I programming language, which proved troublesome during the migration to AIX v3. AIX v2 included full TCP/IP networking, as well as SNA and two networking file systems: NFS, licensed from Sun Microsystems, and Distributed Services (DS). DS had the distinction of being built on top of SNA, and thereby being fully compatible with DS on the IBM midrange AS/400 and mainframe systems. For the graphical user interfaces, AIX v2 came with the X10R3 and later the X10R4 and X11 versions of the X Window System from MIT, together with the Athena widget set. Compilers for Fortran and C were available. One of the more popular desktop applications was the PageMaker desktop publishing software.

IBM PS/2 series

AIX PS/2 (also known as AIX/386) was developed by Locus Computing Corporation under contract to IBM. AIX PS/2, first released in 1989, ran on IBM PS/2 personal computers with Intel 386 and faster processors.

IBM mainframes

In 1988, IBM announced AIX/370, also developed by Locus Computing. AIX/370 was IBM's first attempt to offer Unix-like functionality for their mainframe line, specifically the System/370. AIX/370 was released in 1990 with functional equivalence to System V Release 2 and 4.3BSD as well as IBM enhancements. With the introduction of the ESA/390 architecture, AIX/370 was replaced by AIX/ESA in 1991, which was based on OSF/1, and also ran on the System/390 platform. This development effort was made partly to allow IBM to compete with Amdahl UTS. Unlike AIX/370, AIX/ESA ran both natively as the host operating system, and as a guest under VM. AIX/ESA, while technically advanced, had little commercial success, partially because UNIX functionality was added as an option to the existing mainframe operating system, MVS, which became MVS/ESA OpenEdition in 1999.

POWER/PowerPC-based systems

The release of AIX version 3 (sometimes called AIX/6000) coincided with the announcement of the first IBM RS/6000 models. The RS/6000 was unique in that it not only outperformed all other machines in integer compute performance, but also beat the competition by a factor of 10 in floating-point performance.

Releases of AIX version 3 also took advantage of the developments in the POWER architecture.

AIX v3 innovated in several ways on the software side. It was the first operating system to introduce the idea of a journalling file system, JFS, which allowed for fast boot times by avoiding the need to fsck the disks on every reboot. Another innovation was the introduction of shared libraries, which avoided the need for an application to statically link to the libraries it used. The resulting smaller binaries used less of the hardware RAM, to run, and used less of the disk space to install. Besides improving performance, it was a boon to developers: executable binaries could be in the 10s of kilobytes instead of a megabyte for an executable statically linked to the C library. AIX v3 also ditched the microkernel of AIX v2, a contentious move that resulted in v3 being somewhat more "pure" (and containing no PL/1 code) than v2.

Other notable subsytems included:

IRIS GL, a 3D rendering library, the progenitor of OpenGL. IrisGL was licensed by IBM from SGI, then a small company which had sold only one thousand machines to date. SGI also provided the low-end graphics card for the RS/6000, capable of drawing 20,000 Gouraud-shaded triangles per second. The high-end graphics card was designed by IBM, a follow-on to the mainframe-based IBM 5080, capable of rendering 990K vectors per second.
PHIGS, another 3D rendering API, popular in automotive CAD/CAM circles, and at the core of CATIA.
Full implementation of version 11 of the X Window System, together with Motif as the recommended widget collection and window manager.
Network file systems: NFS from Sun; AFS, the Andrew File System; and DFS, the Distributed File System.
NCS, the Network Computing System, licensed from Apollo Computer (later acquired by HP)
The NeXT windowing system (NeXT DPS). This was notable as a "plan B", in case the X11/Motif/IrisGL combination failed in the marketplace. However, it was highly proprietary: it hadn't been licensed to any other Unix vendor. This, in the face of the open systems challenge of X11/Motif and its lack of 3D capability, cemented its failure in the marketplace.

As of 2007, the current release of AIX runs on the RS/6000 and System p, BladeCenter JS-series, IntelliStation POWER, and System i5 platforms.

Apple Network Servers

The Apple Network Server systems were PowerPC-based systems designed by Apple Computer to have numerous high-end features that standard Apple hardware did not have, including swappable hard drives, redundant power supplies, and external monitoring capability. These systems were more or less based on the Power Macintosh hardware available at the time but were designed to use AIX (versions 4.1.4 or 4.1.5) as their native operating system in a specialized version specific to the ANS.

AIX was only compatible with the Network Servers and was not ported to standard Power Macintosh hardware. Not to be confused is A/UX, Apple's earlier version of Unix for 68k-based Macintoshes.

IA-64 systems

As part of Project Monterey, a beta test version of AIX 5L was released for the IA-64 (Itanium) architecture in 2001, but this was abandoned before it became an official product due to the lack of interest in the finished Project Monterey system, as well as the overall lack of uptake of the IA-64 architecture by a skeptical marketplace, which largely gravitated towards the Project Trillian port of Linux as the primary platform OS.

Versions

POWER/PowerPC releases

AIX 6.1, November 9, 2007

Workload Partitions (WPARs) operating system-level virtualization
Live Application Mobility
Role Based Access Control RBAC
AIX Security Expert - A system and network security hardening tool
Trusted AIX
Integrated Electronic Service Agent(tm) for auto error reporting
Encrypting JFS2 filesystem
Trusted Execution
Concurrent Kernel Maintenance
Kernel exploitation of POWER6 storage keys
ProbeVue dynamic tracing
Systems Director Console for AIX
Integrated filesystem snapshot

AIX 5L 5.3, August 13, 2004

NFS Version 4
Advanced Accounting
Virtual SCSI
Virtual Ethernet
Exploitation of Simultaneous multithreading (SMT)
Micro-Partitioning enablement
POWER5 exploitation
JFS2 quotas
Ability to shrink a JFS2 filesystem
kernel scheduler has been enhanced to dynamically increase and decrease the use of virtual processors. AIX 5L Version 5.3 ML3

AIX 5L 5.2, October 18, 2002

Ability to run on the IBM BladeCenter JS20 with the PowerPC 970.
Minimum level required for POWER5 hardware
MPIO for Fibre Channel disks
iSCSI Initiator software
Participation in Dynamic LPAR
Concurrrent I/O (CIO) feature introduced for JFS2 released in Maintenance Level 01 in May 2003

AIX 5L 5.1, May 4, 2001

Ability to run on an IA-64 architecture processor, although this never went beyond beta,
Minimum level required for POWER4 hardware and the last release that worked on the Micro Channel architecture
64-bit kernel, installed but not activated by default
JFS2
Ability to run in a Logical Partition on POWER4
The L stands for Linux affinity
Trusted Computing Base (TCB)
Support for mirroring with striping

AIX 4.3.3, September 17,1999

Online backup function
Workload Manager (WLM)
Introduction of topas utility

AIX 4.3.2, October 23,1998
AIX 4.3.1, April 24,1998
AIX 4.3, October 31,1997

Ability to run on 64-bit architecture CPUs
IPv6
Web-based System Manager

AIX 4.2.1, April 25,1997

NFS Version 3

AIX 4.2, May 17,1996
AIX 4.1.5, November 8,1996
AIX 4.1.4, October 20,1995
AIX 4.1.3, July 7,1995

CDE 1.0 became the default GUI environment, replacing Motif X Window Manager.

AIX 4.1.1, October 28,1994
AIX 4.1, August 12,1994
AIX 4.0, 1994

Run on RS/6000 systems with PowerPC processors and PCI busses.

AIX 3.2 1992
AIX 3.1, February 1990

Journaled File System (JFS) filesystem type

AIX 3.0 1989

LVM (Logical Volume Manager) was incorporated into OSF/1, and in 1995 for HP-UX, and the Linux LVM implementation is similar to the HP-UX LVM implementation
SMIT was introduced.

IBM PS/2 releases

AIX PS/2 v1.1, 1989

last version was 1.3, 1992.

IBM 6150 RT releases

AIX v1.0, 1986
AIX v2.0

last version was 2.2.1.

User interfaces

Graphical

The Common Desktop Environment (CDE) is AIX's default graphical user interface. As part of Linux Affinity and the free AIX Toolbox for Linux Applications (ATLA), open-source KDE and GNOME desktop are also available.

System Management Console

SMIT is the System Management Interface Tool for AIX. It allows a user to navigate a menu hierarchy of commands, rather than using the command line. Invocation is typically achieved with the command smit. Experienced system administrators make use of the F6 function key which generates the command line that SMIT will invoke to complete the proposed task.

SMIT also generates a log of commands that are performed in the smit.script file. The smit.script file automatically records the commands with the command flags and parameters used. The smit.script file can be used as an executable shell script to rerun system configuration tasks. SMIT also creates the smit.log file, which contains additional detailed information that can be used by programmers in extending the SMIT system.

smit and smitty refer to the same program, though smitty invokes the text-based version, while smit will invoke an X Window System based interface if possible; however, if smit determines that X Window System capabilities are not present, it will present the text-based version instead of failing. Determination of X Window System capabilities is typically performed by checking for the existence of the DISPLAY variable.