What Is AS400?
AS400 is IBM's mid-range business computing platform introduced in 1988. Despite multiple name changes over the decades, AS400 remains the most widely used search term for IBM i, iSeries, and IBM Power systems worldwide.
AS400 is the IBM Application System/400, a mid-range business computer introduced by IBM on June 21, 1988. IBM has renamed the platform multiple times since then. It became the iSeries in 2000, System i in 2006, and is now officially called IBM i ... running on IBM Power Systems hardware. Despite these changes, AS400 remains the dominant term used by IT professionals, executives, and administrators worldwide to describe this class of IBM computing platform.
What Does AS400 Stand For?
AS400 stands for Application System/400. The 400 referred to IBM's internal project number at the time of the platform's design and launch. The Application System designation distinguished it from IBM's mainframe and personal computer product lines. It was positioned as a mid-range business computer, more powerful than a PC, more accessible than a mainframe, with integrated database capabilities built directly into the operating system.
The AS400 Name Timeline
IBM renamed the platform four times over four decades:
- 1988: AS/400 ... Application System/400, introduced at the Rochester, Minnesota lab
- 2000: iSeries ... reflecting IBM's broader "e-business" branding push
- 2006: System i ... part of a unified IBM Systems branding consolidation
- 2008 to present: IBM i ... the operating system name, running on IBM Power Systems hardware
Each name change updated the branding but the core workloads, the integrated database (DB2 for i), the RPG programming language, and the object-based architecture remained. Organizations that installed AS400 hardware in 1992 may now be running IBM i 7.5 on Power10 hardware, but they still call themselves an AS400 shop.
Why Do People Still Call It AS400?
AS400 became embedded in the vocabulary of IT departments worldwide across more than a decade of dominance through the 1990s. Administrators trained on the AS400, developers who wrote RPG programs, and IT managers who built business processes around it carried the terminology forward through every subsequent brand transition.
AS400 is also the Kleenex of IBM midrange computing ... a brand name so dominant it became the generic. Search data confirms that AS400 still drives far more search volume than IBM i or Power Systems for equivalent queries in most global markets.
What Is AS400 Used For?
AS400 and its modern descendants run business-critical workloads across manufacturing, retail, healthcare, banking, insurance, and government. Common workloads include:
- ERP systems (JD Edwards, SAP, Infor)
- Core banking and financial transaction processing
- Warehouse management and supply chain systems
- Healthcare patient record systems
- Government record management
- Payroll and HR systems
The platform's reputation for reliability, security, and uptime is why organizations that adopted it decades ago often see no compelling reason to migrate off it.
Is AS400 Still Relevant?
Yes. IBM i (the modern AS400) continues to receive active development and support from IBM. IBM i 7.5, released in 2022, introduced new capabilities including integration with modern APIs and cloud services. IBM Power11 hardware, launched in 2024, is fully compatible with IBM i and offers significant performance improvements over previous generations.
Thousands of organizations worldwide run IBM i as their primary business computing platform. The question for most AS400 shops is not whether to leave the platform, but how to modernize the experience on top of it.