IBM System i

The IBM System/38 was introduced in July 1980 as a minicomputer for general business and departmental use. It was replaced by the AS/400 midrange computer in 1987 and later re branded 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 re-branding 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.
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-based technologies 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.