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What is an IBM i Server


The IBM System/38 was introduced in November 1979 as a minicomputer for general business and departmental use. It was replaced by the AS/400 midrange computer in 1987 and later rebranded as the eServer iSeries in 2000. It was renamed in 2006 as the IBM System i until April 2008 when it was replaced by the IBM Power Systems line. It uses an object-based operating system called IBM iOS. The operating system has undergone name changes in accordance with the rebranding of the IBM server line. Initially, it was called OS/400 (following the name schema that gave birth to OS/2 and OS/390). Later on became known as i5/OS in line with the introduction of the eServer i5 servers featuring POWER5 processors. Finally, it was called just IBM System  i or IBM i for short coinciding with the 6.1 release.

Features include a DBMS (DB2/400), a menu-driven interface, multi-user support, dumb terminal support (IBM 5250), printers, as well as security, communications and web-based applications, which could be executed either inside the (optional) IBM WebSphere application server or in PHP/MySQL using a native port of the Apache web server.

While in Unix-like systems “everything is a file”, on the System i everything is an object, with built-in persistence and garbage collection. It also offers Unix-like file directories using the Integrated File System. Java compatibility is implemented through a native port of the Java virtual machine.


The IBM System i platform extended the System/38 architecture of an object-based system with an integrated DB2 relational database. Equally important were the virtual machine and single-level storage concepts which established the platform as an advanced business computer.

Instruction set

One feature that contributes to the longevity of the IBM System i platform is its high-level instruction set (called TIMI for "Technology Independent Machine Interface" by IBM), which allows application programs to take advantage of advances in hardware and software without recompilation. TIMI is a virtual instruction set; it is not the instruction set of the underlying CPU. User-mode programs contain both TIMI instructions and the machine instructions of the CPU, thus ensuring hardware independence. This is conceptually somewhat similar to the virtual machine architecture of programming environments such as Smalltalk, Java and .NET. The key difference is that it is embedded so deeply into the AS/400's design as to make applications effectively binary-compatible across different processor families.

Note that, unlike some other virtual-machine architectures in which the virtual instructions are interpreted at runtime, TIMI instructions are never interpreted. They constitute an intermediate compile time step and are translated into the processor's instruction set as the final compilation step. The TIMI instructions are stored within the final program object, in addition to the executable machine instructions. This is how application objects compiled on one processor family (e.g., the original CISC AS/400 48-bit processors) could be moved to a new processor (e.g., PowerPC 64-bit) without re-compilation. An application was saved from the older 48-bit platform and restored onto the new 64-bit platform, where the operating system discarded the old machine instructions and re-translated the TIMI instructions into 64-bit instructions for the new processor.

The IBM System i's instruction set defines all pointers as 128-bit. This was the original design feature of the System/38 (S/38) in the mid 1970s planning for future use of faster processors and an expanded address space. The original AS/400 CISC models used the same 48-bit address space as the S/38. The address space was expanded in 1995 when the PowerPC RISC 64-bit CPU processor replaced the 48-bit CISC processor.

For PowerPC processors, the virtual address resides in the rightmost 64 bits of a pointer while it was 48 bits in the S/38 and CISC AS/400. The 64-bit address space references main memory and disk as a single address set which is the single-level storage concept.


The IBM System i includes an extensive library-based operating system, i5/OS, and is also capable of supporting multiple instances of AIX, Linux, Lotus Domino, Microsoft Windows 2000 and Windows Server 2003. While i5/OS, AIX, Linux and Lotus Domino are supported on the POWER processors, Windows is supported with either single-processor internal blade servers (IXS) or externally-linked multiple-processor servers (IXA and iSCSI). iSCSI also provides support for attachment of IBM Bladecenters. Windows, Linux, and VMWare ESX(VI3) are supported on iSCSI attached servers.

LPAR (Logical PARtitioning), a feature introduced from IBM's mainframe computers, facilitates running multiple operating systems simultaneously on one IBM System i unit. A system configured with LPAR can run various operating systems on separate partitions while ensuring that one OS cannot run over the memory or resources of another. Each LPAR is given a portion of system resources (memory, hard disk space, and CPU time) via a system of weights that determines where unused resources are allocated at any given time. The operating systems supported (and commonly used) under the LPAR scheme are i5/OS, AIX, and Linux.

Other features include an integrated DB2 database management system, a menu-driven interface, multi-user support, non-programmable terminals (IBM 5250) and printers, security, communications, client–server and web-based applications. Much of the software necessary to run the IBM System i is included and integrated into the base operating system.

The IBM System i also supports common client–server systems such as ODBC and JDBC for accessing its database from client software such as Java, Microsoft .NET languages and others.

The IBM System i also provides an environment for AIX applications to run natively on i5/OS without the need for an AIX LPAR.

AIX programs are binary compatible with OS/400 when using OS/400's PASE (Portable Applications System Environment). PASE is essentially "an operating system within an operating system", supporting the most recent stable version of AIX. Binaries need to be re-compiled on the AIX system, with 16-byte (quadword) pointer alignment enabled. Once the program is compiled with this option, it can be executed under the PASE Korn Shell.


Programming languages available for the IBM System i include RPG, RPGIV, RPGILE, assembly language, C, C++, Pascal, Java, EGL, Perl, Smalltalk, COBOL, SQL, BASIC, PHP, PL/I, Python and REXX. Several CASE tools are available: AllFusion Plex (see *Plex Wiki), ADELIA, Synon, AS/SET, IBM Rational Business Developer Extension, LANSA and ProGen Plus.

The IBM System i fully supports the Java language, including a 32-bit Java Virtual Machine (JVM) and a 64-bit JVM.

Commands in the Control Language (CL) are promptable using the keyboard F4 function key, and most provide cursor-sensitive help to make specifying command parameters simpler. All command names and parameter keywords are based upon uniform standardized and mostly 3-letter abbreviations for verbs and subjects, making for easy rendering and interpretation by the application developer, as opposed to other operating systems with often cryptic or inconsistent command names for related functions or command parameter switches. For instance, the parameter keyword to apply a text description to any object to be created or changed is spelled the same way for all such commands.


  • CRTUSRPRF - Create user profile
  • DSPUSRPRF, CHGUSRPRF, DLTUSRPRF - Display, change, and delete user profile
  • DLTLIB - Delete library
  • CRTLIB, DSPLIB, CHGLIB - Create, display, and change a library
  • ADDLIBLE, CHGLIBL - Add to or change library list
  • CPYF, CRTF, DSPF, CHGF, DLTF - Copy, create, display, change, and delete file
  • WRKACTJOB - Work with Active Jobs
  • WRKSYSSTS - Work with System Status
  • STRSST, STRPASTHR, STRSBS - Start System Service Tools, start pass through (remote login), start subsystem
  • VRYCFG - Vary configuration, bring interfaces up or down
  • PWRDWNSYS - Power Down System
  • WRKSPLF - Work with spool files

For traditional business programming languages such as RPG, COBOL, and C, the IBM System i provides an interface to the integrated database that allows these languages to treat database files much like other platforms treat ISAM or VSAM files.

Support for 5250 display operations is provided via display files, an interface between workstations, keyboards and displays, and interactive applications, as opposed to batch processing with little or no user interaction. ASCII terminals and PC workstations are equally and well supported, also via internet or LAN network access supplemented by either IBM or non-IBM communication software, for example TELNET or TELNET 5250.


The IBM System i, then known as the AS/400, was the continuation of the System/38 database machine architecture (announced by IBM in October 1978 and delivered in August 1979). The AS/400 removed capability-based addressing. The AS/400 added source compatibility with the System/36 combining the two primary computers manufactured by the IBM Rochester plant. The System/36 was IBM's most successful mini-computer but the architecture had reached its limit. The first AS/400 systems (known by the development code names Silverlake and Olympic) were delivered in 1988 under the tag line "Best of Both Worlds" and the product line has been refreshed continually since then. The programmers who worked on OS/400, the operating system of the AS/400, did not have a UNIX background. Dr Frank Soltis, the chief architect, says that this is the main difference between this and any other operating system.

The AS/400 was one of the first general-purpose computer systems to attain a C2 security rating from the NSA (Gould UTX/C2, a UNIX-based system was branded in 1986), and in 1995 was extended to employ a 64-bit processor and operating system.

The 1995 change-over from 48 to 64-bit required that all programs be 'observable', i.e. that the debugging information had not been stripped out of the compiled code. This caused problems for those who had bought third-party products that had no source and no observability. In 2008, the introduction of V6R1 caused similar problems, although this time IBM preferred to call it a "refresh".[1]

In 2000 IBM renamed the AS/400 to iSeries, as part of its e-Server branding initiative. The product line was further extended in 2004 with the introduction of the i5 servers, the first to use the IBM POWER5 processor. The architecture of the system allows for future implementation of 128-bit processors when they become available.

Although announced in 1988, the IBM System  i remains IBM's most recent major architectural shift that was developed wholly internally. Since the arrival of Lou Gerstner in 1993, IBM has viewed such colossal internal developments as too risky. Instead, IBM now prefers to make key product strides through acquisition (e.g., the takeovers of Lotus Software and Rational Software) and to support the development of open standards, particularly Linux. It is noteworthy that after the departure of CEO John Akers in 1993, when IBM looked likely to be split up, Bill Gates commented that the only part of IBM that Microsoft would be interested in was the IBM System  i division. (At the time, many of Microsoft's internal systems ran on the IBM System  i platform.)


The  was originally based on a custom IBM CISC CPU which used a CPU architecture known as Internal MicroProgrammed Interface (IMPI) and an instruction set similar to the IBM 370. It was later migrated to a POWER-based RISC CPU family eventually known as RS64.


Source : Wikipedia


Last Updated (Monday, 12 July 2010 18:49)

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