IBM AS/400 | 1988
IBM AS/400
The IBM AS/400 (Application System/400) is a family of midrange computers from IBM that was announced in June 1988 and released in August 1988. It succeeded the System/36 and System/38 platforms and ran the OS/400 operating system. More affordable yet more powerful than its predecessors, the AS/400 was highly successful at launch, with an estimated 111,000 units installed by the end of 1990, and annual revenue reaching $14 billion that year. By 1994, the number of units had increased to 250,000, and approximately 500,000 units were shipped by 1997.
A key concept in the AS/400 platform is the Technology Independent Machine Interface (TIMI), a platform-independent instruction set architecture (ISA) that is translated into native machine language instructions. This allowed the platform to change its underlying processor architecture without breaking application compatibility. Early systems were based on a 48-bit CISC instruction set architecture known as the Internal Microprogrammed Interface (IMPI), originally developed for the System/38. In 1991, IBM introduced a new version of the system running on a series of 64-bit PowerPC-based CPUs, the IBM RS64 family. Due to TIMI, applications written for the original CISC-based systems continued to run on the new systems without modification, as the TIMI code could be re-translated into the new system's PowerPC native machine code. The RS64 was eventually replaced by the POWER4 processors in 2001, followed by POWER5 and POWER6 in later generations.
The AS/400 went through multiple rebranding exercises and was eventually renamed the System i in 2006. In 2008, IBM consolidated the separate System i and System p product lines into a single product line called IBM Power Systems. The name "AS/400" is sometimes informally used to refer to the IBM i operating system running on modern Power Systems hardware.
In the early 1980s, IBM management became concerned that the large number of incompatible midrange computer systems was hindering IBM's competitiveness, particularly against Digital Equipment Corporation’s VAX. In 1982, IBM started a project called Fort Knox, aimed at consolidating the System/36, System/38, IBM 8100, Series/1, and the IBM 4300 series into a single product line based around an IBM 801-based processor codenamed Iliad. This would allow backward compatibility with the systems it replaced, and the project also aimed to create a new operating system.
However, the Fort Knox project was overly ambitious and faced numerous delays. When the engineers attempted to port the operating systems and software from the existing platforms, they realized it would be impossible without making extensive modifications to the Iliad processor. The proposed solution was to augment Iliad with co-processors designed for each operating system, but these co-processors became so complex that they essentially took over the role of the main processor, leaving Iliad as a support processor. Ultimately, the Fort Knox project was canceled in 1985.
As Fort Knox stalled, engineers in IBM Rochester began an unofficial project that eventually became the official Silverlake project, which sought to create a replacement for both the System/36 and System/38 in the shortest possible time. This project became the foundation of the AS/400, which was officially announced on June 21, 1988. The AS/400 operating system was named OS/400.
In 1990, IBM started working to replace the AS/400’s original 48-bit CISC processors with a 96-bit architecture called C-RISC (Commercial RISC). However, in 1991, at the request of IBM president Jack Kuehler, a proposal was delivered to adapt the 64-bit PowerPC architecture to meet AS/400’s needs. This led to the creation of the Amazon (later PowerPC AS) extensions to the PowerPC architecture.
AS/400 processors evolved over time with the introduction of Cobra and Muskie processors for low-end and high-end systems, respectively. These processors formed the basis of the IBM RS64 family, which eventually merged with the POWER architecture in the POWER4 processors. Despite these changes, the TIMI architecture hid the differences from users and allowed applications to run on newer processors without modification.
The AS/400 went through several rebrandings, such as AS/400 Advanced Series in 1994, AS/400e in 1997, and eventually eServer iSeries in 2000. In 2004, the product line was renamed eServer i5, and in 2006, it was rebranded as System i. Finally, in 2008, IBM merged the System i and System p lines into a unified product called IBM Power Systems.
Though announced in 1988, the AS/400 remains IBM’s most recent major architectural shift developed entirely in-house. In 1993, after the departure of CEO John Akers, when IBM was at risk of being split up, Bill Gates remarked that Microsoft would only be interested in the AS/400 division.
