Aug 6, 2010 As400

The IBM System i is IBM’s previous generation of mid-range computer systems for IBM i users, and was subsequently replaced by the IBM Power Systems in April 2008.
The platform was first introduced as AS/400 in 1987 and later renamed as the eServer iSeries in 2000. As part of IBM’s Systems branding initiative in 2006, it was again renamed to System i.
In April 2008, IBM announced its integration with the System p platform. The unified product line is called IBM Power Systems and features support for the IBM i (previously known as i5/OS or OS/400), AIX and Linux operating systems. Power4 or older hardware ran OS/400 exclusively.
Summary
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 i 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[1] 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.[2] Java compatibility is implemented through a native port of the Java virtual machine.
Features
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.
[edit] 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.
[edit] Software
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.