IBM System i

The IBM System i is a family of midrange computers from IBM. It was first introduced as the AS/400 (Application System/400) in June 1988, alongside the OS/400 operating system. It was intended as the successor to IBM's System/36 and System/38 platforms. Early AS/400 systems used the same IMPI architecture as the System/38, but later systems moved to the PowerPC-based IBM RS64.
It was re-branded multiple times by IBM - first as the AS/400 Advanced Series in 1994, followed by AS/400e (the "e" standing for e-business) in 1997, eServer iSeries in 2000, eServer i5 (along with OS/400 becoming i5/OS) in 2004, and finally System i in 2006.
In April 2008, System i and System p were consolidated into the IBM Power Systems platform. The i5/OS operating system was rebranded to IBM i, and retained full backwards compatibility with the previous hardware platforms.
Summary.
The predecessor to AS/400, IBM System/38, was first made available in August 1979 and was marketed as a minicomputer for general business and departmental use. It was sold alongside other product lines, each with a different architecture (System/3, System/32, System/34, System/36).
Realizing the importance of compatibility with the thousands of programs written in legacy code, IBM launched the AS/400 midrange computer line in 1988. AS stands for "Application System." Great effort was made during development of the AS/400 to enable programs written for the System/34 and System/36 to be moved to the AS/400. Programs on the System/38 were directly compatible with the new AS/400 (after they were 're-encapsulated' by the operating system).
In 2000, in accordance with IBM's eServer initiative, the AS/400 series was rebranded as the eServer iSeries. In 2006, it was again rebranded as the IBM System i. In 2008, almost 20 years after being introduced, the System i and IBM System p product lines were combined into a new product line called the IBM Power Systems line.
The AS/400 operating system was originally named OS/400 (following the pattern begun with OS/360 and followed with OS/2). The operating system has undergone name changes along with the rebranding of IBM's server lineup. The operating system was rebranded as i5/OS to correspond with the introduction of POWER5 processors and the rebranding of the hardware to eServer iSeries. In 2008, the operating system was rebranded to IBM i, with the introduction of the IBM Power Systems.
The operating system is object-based. Features include a RDBMS (DB2/400), a menu-driven interface, support for multiple users, block-oriented terminal support (IBM 5250), and printers. IBM i has built-in security, and support for communications, and web-based applications which can be executed inside the optional IBM WebSphere Application Server or as PHP/MySQL applications inside a native port of the Apache web server.
Unlike the "everything is a file" feature of Unix and its derivatives, on IBM i everything is an object (with built-in persistence and garbage collection). IBM i offers Unix-like file directories using the Integrated File System. Java compatibility is implemented through a native port of the Java virtual machine.
Like IBM's mainframe operating systems, IBM i uses EBCDIC as the inherent encoding.
OS/400 Version 4, Release 4 (V4R4) introduced LPARs (logical partitions) allowing multiple virtual systems to run on a single hardware footprint.
Features.
The IBM System i platform extended the System/38 architecture of an object-based system with an integrated DB2 relational database. Equally important are the virtual machine and single-level storage concepts which established the platform as an advanced business computer.
Instruction set.
One feature that has contributed 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 independent of the underlying machine instruction set of the 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 Java and .NET.
Unlike some other virtual-machine architectures in which the virtual instructions are interpreted at run time, 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 saved from the older 48-bit platform can simply be restored onto the new 64-bit platform where the operating system discards the old machine instructions and re-translates the TIMI instructions into 64-bit instructions for the new processor.
The system'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, memory and an expanded address space. When at a point in the future 128-bit general purpose processors would appear, IBM i will already be fully 128-bit enabled. 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 RISC PowerPC RS64 64-bit CPU processor replaced the 48-bit CISC processor.
For 64-bit 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.
Software.
The IBM System i includes an operating system originally known as OS/400, later as i5/OS and IBM i. System i is also capable of supporting multiple instances of AIX, Linux, Lotus Domino, Microsoft Windows 2000 and Windows Server 2003. While OS/400, 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 IBM i, 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.
History.
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, named for Silver Lake in downtown Rochester, Minnesota, where development of the system took place, 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 IMPI, with 48-bit addresses, to PowerAS, with 64-bit addresses, 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 release of i5/OS V6R1 (later known as IBM i 6.1) caused similar problems due to changes to the TIMI in that release.
In 2000, IBM renamed the AS/400 to iSeries, as part of its e-Server branding initiative. At that time, it adopted more PC server-like features, such as PS/2 keyboards and mice and VGA video output, mostly coming from IBM PS/2 and Intel server line (called eServer xSeries), replacing proprietary technologies. In 2001, it switched to the POWER4 processor from the PowerAS processors used by previous generations.
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 AS/400 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. 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 AS/400 division. (At the time, many of Microsoft's business and financial systems ran on the AS/400 platform, something that ceased to be the case around 1999, with the introduction of Windows 2000.)
Hardware.
The AS/400 was originally based on a custom IBM CISC CPU which had an instruction set architecture, known as "Internal Microprogrammed Interface" (IMPI), similar to that of the IBM System/370. It was later migrated to a POWER-based RISC CPU family eventually known as RS64.
CPU in AS/400, iSeries, i5, Power Systems.
The System i5 used POWER CPUs, which were developed and manufactured by IBM. The POWER 4/5/5+ chips contain two cores. There are Multi-Chip Modules (MCM) available. They have 2 CPUs (4 cores) or 4 CPUs (8 cores) in one MCM. 