IBM AS/400
| Company type | Product line |
|---|---|
| Industry | Computer hardware |
| Predecessor | System/36, System/38 |
| Founded | June 1988 |
| Products | Midrange computer systems |
| Owner | IBM |
The IBM AS/400 (short for Application System/400) represents a series of midrange computers introduced by IBM in June 1988, with market availability beginning in August of the same year. This line succeeded the System/36 and System/38 models, operating on the OS/400 platform. Designed as a cost-effective yet more capable alternative to earlier systems, it achieved approximately 111,000 installations by 1990, generating around $14 billion in yearly revenue. By 1994, the installed base expanded to 250,000 units, and by 1997, shipments reached close to half a million.
A distinctive aspect of the AS/400 is its use of the Technology Independent Machine Interface (TIMI), an instruction set architecture that abstracts hardware specifics, translating into native machine code. This innovation allowed IBM to upgrade processor designs without disrupting application compatibility. Initial models operated on a 48-bit CISC instruction set known as Internal Microprogrammed Interface (IMPI), originally developed for the System/38. In 1995, IBM transitioned to processors based on 64-bit PowerPC derivatives, which later evolved into the IBM RS64 series. Thanks to TIMI's abstraction layer, software written for the original CISC architecture ran seamlessly on these newer CPUs. The RS64 was succeeded by the POWER4 processor family in 2001, followed by upgrades to POWER5 and POWER6 processors.
Throughout its lifecycle, the AS/400 was rebranded multiple times, adopting the name System i in 2006. In 2008, IBM consolidated the System i and System p product lines—already closely aligned in hardware—into a single platform called IBM Power Systems. Despite these changes, the term "AS/400" remains commonly used informally to describe the IBM i operating system running on contemporary Power Systems equipment.
Fort Knox
In the early 1980s, IBM aimed to unify its fragmented and incompatible midrange computer offerings to strengthen its competitive stance against Digital Equipment Corporation's VAX. The Fort Knox project, initiated in 1982, sought to merge the System/36, System/38, IBM 8100, Series/1, and IBM 4300 families into a single product line built around an Iliad processor derived from the IBM 801. The goal was to preserve backward compatibility while developing a new operating system alongside ports of existing OSes for customer transition.
However, Fort Knox proved overly complex and ambitious, leading to delays and scope cuts such as eliminating support for IBM 8100 and Series/1 software. Attempts to port existing operating systems revealed that significant hardware modifications would be necessary for each OS—a requirement rejected by Iliad's designers. The workaround involved incorporating OS-specific co-processors; however, these co-processors ultimately became primary processors themselves while relegating Iliad to ancillary roles. This outcome undermined the consolidation objective, resulting in Fort Knox’s cancellation in 1985.
Silverlake
During Fort Knox's development, a skunkworks team at IBM Rochester created software enabling System/36 applications to operate on System/38 hardware. Following Fort Knox's termination, this initiative evolved into Silverlake, officially launched in December 1985 as a unified hardware solution intended to replace both System/36 and System/38 platforms. Silverlake’s hardware built upon System/38 technology while integrating select innovations from Fort Knox.
Silverlake prioritized rapid deployment to address midrange market needs left unmet due to Fort Knox delays. In 1986, IBM promoted the System/370-compatible IBM 9370 as its preferred midrange system; however, it did not achieve commercial success. Similar to Silverlake, the 9370 reused Fort Knox’s co-processor as its main CPU and utilized the SPD I/O bus architecture derived from Series/1 technology.
AS/400
IBM unveiled the Silverlake system on June 21, 1988, branding it as the Application System/400 (AS/400). This launch included over a thousand software solutions developed by IBM and its partners. The system operated on the Operating System/400 (OS/400). The AS/400 designation followed IBM's naming convention, which prefixed "System" with market-specific identifiers—such as Personal System/2—and distinguished model numbers by system category: two digits for personal computers, three digits for midrange systems like the AS/400, and four digits for mainframes.
Transition to PowerPC
In February 1990, IBM introduced the RS/6000, which utilized RISC technology to deliver enhanced price-to-performance ratios compared to the AS/400. Industry experts interpreted this move as IBM positioning its proprietary AS/400 alongside the Unix-based RS/6000 to compete within midrange segments. It is reported that IBM Rochester sought to restrict the RS/6000’s market appeal to safeguard the AS/400’s position.
That same year, IBM Rochester began substituting the AS/400’s original 48-bit CISC processors with a novel 96-bit architecture called C-RISC, which integrated RISC and VLIW instruction sets while preserving backward compatibility via the System/370-style Internal Microprogrammed Interface (IMPI).
In 1991, under the leadership of Frank Soltis and at the behest of IBM president Jack Kuehler, a development team proposed adopting the 64-bit PowerPC architecture tailored for AS/400 requirements. This initiative led to the creation of the Amazon extensions (later known as PowerPC AS), which IBM selected over C-RISC. These enhancements enabled features such as tagged memory and decimal arithmetic essential for business applications.
IBM initially planned to merge AS/400 and high-end RS/6000 processors through the Belatrix project but abandoned it due to scheduling setbacks. Instead, IBM engineered two distinct processors dedicated to AS/400: Cobra targeting entry-level systems and Muskie aimed at high-performance models, launching the RS64 processor family. The RS64 line developed independently until its integration with the POWER series via POWER4.
Although transitioning from IMPI to PowerPC architecture, the AS/400’s Technology Independent Machine Interface (TIMI) protected users and applications by automatically recompiling software. Migrating OS/400 to this new architecture required extensive rewriting beneath TIMI, resulting in System Licensed Internal Code (SLIC), a reimplemented lower-level operating system primarily coded in C++.
Rebranding
Throughout the 1990s and 2000s, the AS/400 platform experienced multiple rebranding phases aligned with hardware and operating system advancements. In 1994, IBM introduced new models under the AS/400 Advanced Series label, followed by the AS/400e in 1997—the "e" reflecting emphasis on e-business capabilities.
The year 2000 saw IBM launch the eServer iSeries as part of its broader eServer portfolio, transitioning to POWER4 processors shared with the pSeries platform running AIX. By 2004, the iSeries brand was succeeded by eServer i5, marking adoption of POWER5 processors and renaming OS/400 to i5/OS. Over time, hardware designs between iSeries and pSeries converged significantly; their primary difference lay in operating systems. Certain i5 servers supported both AIX and i5/OS through logical partitioning managed by the POWER hypervisor.
The final renaming occurred in 2006 when IBM rebranded eServer i5 as System i. In April 2008, IBM unified System i with System p into the IBM Power Systems family, introducing POWER6 processors. Simultaneously, i5/OS was renamed IBM i to distance it from specific processor generations. Today, IBM i is offered alongside AIX and Linux as one of several operating system choices available on Power Systems, reflecting a strategic emphasis on platform versatility.
Legacy
Introduced in 1988, the AS/400 represents IBM's latest significant architectural innovation developed entirely within the company. Following the exit of CEO John Akers in 1993 during a period when IBM faced potential dissolution, Bill Gates remarked that Microsoft's primary focus within IBM would be the AS/400 division. At that point, numerous Microsoft business and financial applications operated on the AS/400 platform, which was gradually phased out around 1999 coinciding with the release of Windows 2000.
System architecture
As explained by Frank Soltis, one of the principal architects of the AS/400, its design is governed by five core principles that largely stem from the System/38 heritage.
Technology Independence
The system’s high-level instruction set, known as TIMI ("Technology Independent Machine Interface"), allows applications to benefit from advancements in hardware and software without requiring recompilation. TIMI functions as a virtual instruction set distinct from the CPU's native machine instructions. User-level programs embed both TIMI and CPU-specific instructions, providing hardware abstraction similar to virtual machine environments like Java and .NET.
Unlike virtual machines that interpret instructions during execution, TIMI commands are translated into processor-specific code at compile time. The TIMI instructions remain embedded within the final executable alongside native machine code, enabling applications compiled for earlier processors (such as 48-bit CISC architectures) to run effortlessly on newer processors (like 64-bit PowerPC) without recompilation. Upon migration, the operating system discards outdated machine code and recompiles TIMI into instructions suitable for the new CPU.
All pointers in the system are defined as 128-bit—an architectural choice inherited from the mid-1970s IBM System/38—anticipating future processor speed increases and memory expansion. Initially, AS/400 utilized a 48-bit address space akin to S/38; this was extended in 1995 with the transition to 64-bit PowerPC RS64 processors.
Software integration
OS/400 (currently known as IBM i) serves as the native operating system for the AS/400 platform and was originally the exclusive OS supported on its hardware. Many sophisticated features of the AS/400 are embedded within the operating system rather than relying solely on hardware improvements, evolving considerably over time. Notable capabilities include an integrated RDBMS (Db2 for i), a menu-driven user interface, multi-user functionality, compatibility with block-oriented terminals (IBM 5250), and printer support.
Object-based design
In contrast to Unix’s philosophy of "everything is a file," IBM i adopts an object-oriented approach where all entities are treated as objects with inherent persistence and automated garbage collection.
Single-level store
IBM’s single-level store architecture merges main memory and disk storage into a unified address space within its virtual memory model. For 64-bit PowerPC processors, pointers utilize the lower 64 bits for virtual addressing, building upon earlier implementations that used 48 bits.
Hardware integration
Subsequent hardware iterations accommodate multiple guest operating systems such as SSP, AIX, Linux, and Microsoft Windows 2000/Windows Server 2003. OS/400, AIX, and Linux operate on POWER processors through LPARs, whereas Windows runs on single-processor internal blade servers or externally connected multi-processor servers. SSP guests were emulated on OS/400 versions V3R6 through V4R4 by utilizing the Advanced 36 Machine functionality.
CPUs
| CPU | Release Year | Clock Frequency | Associated Server Models | |
|---|---|---|---|---|
| IMPI[note 1] | 1988 | >22 MHz[note 2] | rowspan="5" Template:Version | Bxx, Cxx, Dxx, Exx, Fxx, Pxx, 100, 135, 140, 2xx, 3xx |
| Cobra (A10) | 1995 | 55 or 75 MHz | 4xx, 5xx | |
| Muskie (A25/A30) | 1996 | 125 or 154 MHz | 53x | |
| Apache (RS64) (A35) | 1997 | 125 MHz | 6xx, 150 | |
| NorthStar (RS64 II) | 1998 | 200, 255 or 262 MHz | 170, 250, 7xx, 650, S40, SB1 | |
| Pulsar (RS64 III) | 1999 | 450 MHz | rowspan="8" Template:Version | 270, 820 |
| IStar (RS64 III enhanced) | 2000 | 400, 500, 540 or 600 MHz | 820, 830, 840,[1] SB2, SB3 | |
| SStar (RS64 IV) | 2000 | 540, 600 or 750 MHz | 270, 800, 810, 820, 830, 840 | |
| POWER4 | 2001 | 1.1 or 1.3 GHz | 890 | |
| POWER4+ | 2003 | 1.9 GHz | 825, 870 | |
| POWER5 | 2004 | 1.5 or 1.9 GHz | i5-520; i5-550; i5-570; i5-595 | |
| POWER5+ | 2005 | 1.5 to 2.3 GHz | i5-520, i5-550, i5-515, i5-525; i5-570 | |
| POWER6 | 2007 | 3.5 to 4.7 GHz | BladeCenter JS12, JS22; i5-570 (MMA); M50, M25 & M15 |
System models
| Model Designation | Introduction Year | CPU Classification | Base - CPW |
|---|---|---|---|
| B10, B20, B30, B35, B40, B45, B50, B60, B70 | 1988-1989 | P10, P20 | 2.9 - 20 |
| C04, C06, C10, C20, C25 | 1990 | P10 | 3.1 - 6.1 |
| D02, D04, D06, D10, D20, D25, D35, D45, D50, D60, D70, D80 | >1991 | >P10 to P30 | >3.8 - 56.6 |
| >E02 to E95 series | >1992 | >P10 to P40 | >4.5 - 116.6 |
| >F02 to F97 series | >1993 | >P05 to P40 | >5.5 - 177.4 |
| >P01 to P03 | >1993-1995 | >P05 | >7.3 - 16.8 |
| >150 | >1996 | >P05 | >10.9 - 35.0 |
| >S10 to S40 | >1997 | >P05 to P50 | >45.4 - 4550 |
| >SB1 to SB3 | >1997-2000 | >P30 to P40 | >1794 - 16500 |
| >10S to 140 series | >1993-1995 | >P05 to P20 | >17.1 - 65.6 |
| >170 | >1998 | >P05 to P20 | >30 - 1090 |
| >200 to 236 series | >1994 | >P05 to P10 | >7.3 - 17.1 |
| >250 | >2000 | >P05 | >50 - 75 |
| >270 | >2000 | >P05 to P20 | >50 - 2350 |
| >300 to 310 series | >1994 | >P10 to P40 | >11.6 -177.4 |
| >400 series (400 to 436) | >1995 | >P05 to P10 | >13.8 - 91.0 |
| >500 series (500 to 53S) | >1995 | >P10 to P40 | >18.7 -650 |
| 600 series (600 to650) | 1997 | P05 to P50 | 22.7 -4550 |
| 720 | 1999 | P10 to P30 | 240 -1600 |
| 730 | 1999 | P20 to P40 | 560 -2890 |
| 740 | 1999 | P40 to P50 | 3660 -4550 |
| 800 | 2003 | P05 to P10 | 300 -950 |
| 810 | 2003 | P10 to P20 | 750 -2700 |
| 820 | 2000-2001 | P05 to P40 | 100 -3700 |
| 825 | 2003 | P30 | 3600 -6600 |
| 830 | 2000-2002 | P20 to P50 | 1850 -7350 |
| 840 | 2000-2002 | P40 to P50 | 10000 -20200 |
| 870 | 2002 | P40 to P50 | 7700 -20000 |
| 890 | 2002 | P50 to P60 | 20000 -37400 |
| '520' | '2004-2006' | 'P05 to P20' | '500 -7100' |
| '550' | '2004-2006' | 'P20' | '3300 -14000' |
| '570' | '2004-2006' | 'P30 to P40' | '3300 -58500' |
| '595' | '2004-2006' | 'P50 to P60' | '24500 -216000' |
| '515' | '2007' | 'P05' | '3800 -7100' |
| '525' | '2007' | 'P10' | '3800 -7100' |
| '570' (updated model) | '2007' | 'P40' | '16700 -58500' |
| 'MMA (9406)' | '2007' | 'P30' | '5500 -76900' |
| 'M15' | '2008' | 'P05' | '4300' |
| 'M25' | '2008' | 'P10' | '4300 -8300' |
| 'M50' | '2008' | 'P20' | '4800 -18000' |
| 'MMA' | '2008' | 'P30' | '8150 -76900' |
| 'JS12' | '2008' | 'P05' | '7100' |
| 'JS22' | '2008' | 'P10' | '13800' |
| 'JS23', 'JS43' | '2008' | ||
| '570 (9117)' | '2008' | 'P30' | '104800' |
| '595 (9119)' | '2008' | 'P60' | '294700' |
External links
- IBM Power Systems official page
- IBM Historical Archives:
- AS/400 Advanced Series Handbook (PDF)
Cite error: <ref> tags exist for a group named "note", but no corresponding <references group="note"/> tag was found
- ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).