AS400 Basics FAQ

AS400 is IBM's mid-range business computing platform, introduced in June 1988. The official name is the Application System/400. IBM later renamed it iSeries (2000), System i (2006), and IBM i (2008). The hardware platform became IBM Power Systems. Despite the name changes, AS400 remains the most widely used term for this class of IBM computing.

In common usage, yes. Both terms refer to the same IBM midrange platform lineage. Technically, IBM i is the current name for the operating system (successor to OS/400), while Power Systems is the current hardware. AS400 was the original 1988 hardware brand. Most IT professionals use AS400 and IBM i interchangeably.

IBM i (the modern AS400) is actively supported. IBM i 7.3 is supported through April 2026, 7.4 through April 2028, and 7.5 through April 2030. Original AS400 hardware from the 1980s-1990s is not supported and is long past end of life. Modern IBM Power Systems hardware running current IBM i releases is fully supported.

IBM renamed and evolved the AS400 into iSeries, then System i, then separated into IBM i (the OS) on IBM Power Systems (the hardware). IBM Power11, released in 2024, is the current hardware generation. IBM i 7.5, released in 2022, is the current OS release. Nothing replaced AS400 from outside IBM. IBM continued developing the platform.

They are the same platform at different points in time. AS400 was the original 1988 name. iSeries was the 2000-2006 name. System i was the 2006-2008 name. IBM i is the current OS name (since 2008), running on IBM Power Systems hardware. The application code, database architecture, and OS lineage are continuous across all naming periods.

IBM i (the modern AS400 OS) runs on IBM Power Systems hardware (Power9, Power10, Power11). It does not run on the original AS400 hardware from the 1980s or 1990s, and it does not run on x86 servers or standard cloud infrastructure natively. Power hardware is the only supported IBM i platform.

IBM i supports multiple languages including RPG (the native language), COBOL, CL (Control Language), C, C++, Java, and Python. RPG (specifically ILE RPG or RPGLE) is the most common language in legacy AS400 applications. SQL is widely used for database operations. Most new IBM i development uses a mix of ILE RPG, SQL, and modern integration layers.

Manufacturing, financial services (banking, insurance, credit unions), healthcare, retail, distribution, and government are the primary industries with significant IBM i (AS400) deployments. The platform dominates in environments where transaction reliability, data integrity, and multi-decade application stability are priorities.

IBM i is accessed via 5250 terminal emulation software. Common AS400 terminal emulators include IBM Access Client Solutions (ACS, the current IBM-supported option), IBM Personal Communications (legacy), and third-party options like Mochasoft and TN5250. Modern IBM i environments also support web browser access and API integration for users who do not need the 5250 interface.

Green screen refers to the character-based 5250 terminal interface used to operate AS400 and IBM i systems. Named for the original green phosphor monitors. Green screen modernization is the process of adding a web or GUI front-end to IBM i applications while preserving the underlying business logic on IBM i.