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AS/400, iSeries, eServer Systems

IBM’s Application System/400 (AS400) platform, also called IBM System I, is IBM’s previous design of mid range computer systems for IBM I users. It was first introduced as the AS400 System and later renamed eServer iSeries, before finally being named System i. IBM’s AS400 System was one of the first successful general-purpose computer systems that offers an integrated operating system, database, and middleware built for businesses. The system is designed to support multiple applications and processes with reliability, ensuring a high performance, integrated business service. AS 400 offers easy-to-use computers designed for small and intermediate-sized business companies

Previously Used AS400 Systems

IBM introduced AS 400 Systems in 1988 as a part of their worldwide announcement of more than 1,000 software packages in the biggest simultaneous applications announcement for computers. The AS400 models include six processor designs that offered a 24-fold growth range in main memory, a 48-fold storage capacity range, and a 10-fold performance range. The original AS400 system was a combination of IBM’s popular System 38 and System 36 merged together, and was based on a custom IBM CISC CPU which used a CPU structure known as Internal MicroProgrammed Interface (IMPI). It was later switched to a Power-based RISC CPU.


The AS400 uses the PowerPC microprocessor with a reduced instruction set computer technology. The operating system used is called the OS/400 that provides multi-terabytes of disk storage and a Java virtual memory. The function of the AS400 was to provide a versatile server that can replace PC servers and Web servers that compete with both Wintel and UNIX servers.

Some other great features provided by the AS400 operating system includes its data warehousing, java application development, web and e-commerce serving, and corporate groupware services. With these additional features, AS400 can hold large amounts of company data as well as an improved application development system designed for building commercial applications with Java.

The AS 400 System is one of IBM’s most successful systems, widely installed in many large business enterprises, small corporations, and a variety of industry segments over the years. AS400 provides its customers with thousands of applications that have been written and web-enabled.


Over the years, the AS400 has been changed and improved significantly. One of the biggest changes occurred in 2008, when the IBM I operating system was combined with IBM’s AIX Unix operating system and Linux onto the same Power server systems. Additionally, in 2013 IBM I integrated with the open source PHP language to further enhance the platform’s performance. The multi-OS feature of the system also is ensured by the implementation of the PowerVM virtualization technology, allowing it to drive the highest efficiency in its performance.

The AS400 product line was later extended to the first use of the IBM Power5 processor after being renamed to iSeries, and later transitioning to the popular Power Systems.