What Is an AS400 System?

By Laura Gittins

The AS/400 is a series of computers that was manufactured and distributed by IBM beginning in 1988. The name AS/400 stands for Application System/400. IBM designed them for small and mid-size businesses. The AS/400 models were renamed as the iSeries in 2000 and then the System i in 2006.


The original six B-series computers released in 1988 were named B10 through B60. In 1989, IBM released the B70, which had a faster processor and improved memory speeds, as well as other processor models. The B70 also allowed more workstations and communication lines to attach to it. Throughout the 1990s, IBM continued to expand the AS/400 line, releasing hardware and software products with more efficient processors, improved operating systems, memory management and data storage.


Upon its release, the AS/400 series featured six different models, and the ability to expand main memory up to 24 times and storage capacity up to 48 times. The most distinguishing feature of each subsequent release in the line were new, low-cost processors that improved performance, including the E model processors released in 1992. These were the computer industry's first 16-million bit memory chips. In 1993, IBM released three high-performance servers under the AS/400 series.

Operating System

The original operating system released on AS/400 models was the OS/400. The AS/400 series replaced IBM's System/38 and System/36 product lines, and the OS/400 was an updated version of the operating systems used on these computers. As such, developers of the OS/400 made the operating system backwards-compatible with these older machines. Descendants of the OS/400 operating system remain in development and supported by IBM. IBM renamed OS/400 as IBM i in 2008.


When IBM first released the AS/400 series, approximately 2,500 software applications were released simultaneously, ranging from business to educational programs. Within the first nine years of its release, IBM sold more than 400,000 AS/400 units. The AS/400 was the last system IBM built internally. Since 1993, IBM's primary developments have come as a result of acquisitions of other companies. The AS/400 was also the first general-purpose system to receive a C2 rating from the National Security Agency. A C2 rating defines how safely a system operates and ensures secure logins and controlled access to a system.