IBM System i

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
IBM System i
IBM AS-400 9406-730.jpg
IBM AS/400e model 730
Also known asAS/400, iSeries
TypeMidrange computer
Release date1988 (as AS/400)
2000 (as eServer iSeries)
DiscontinuedSep 30, 2013
Operating systemOS/400 (later known as i5/OS and IBM i)
PredecessorIBM System/38,
IBM System/36
SuccessorIBM Power Systems running IBM i
Related articlesIBM System p

The IBM System i is a family of midrange computers from IBM. It was first introduced as the AS/400 (Application System/400) in June 1988, alongside the OS/400 operating system. It was intended as the successor to IBM's System/36 and System/38 platforms. Early AS/400 systems used the same IMPI architecture as the System/38, but later systems moved to the PowerPC-based IBM RS64.

It was re-branded multiple times by IBM - first as the AS/400 Advanced Series in 1994, followed by AS/400e (the e standing for e-business) in 1997,[1] eServer iSeries in 2000,[2] eServer i5 (along with OS/400 becoming i5/OS) in 2004, and finally System i in 2006.

In April 2008, System i and System p were consolidated into the IBM Power Systems platform. The i5/OS operating system was rebranded to IBM i, and retained full backwards compatibility with the previous hardware platforms.[3]


IBM AS/400
IBM System i 570 server (as of 2006)

The predecessor to AS/400, IBM System/38, was first made available in August 1979 and was marketed as a minicomputer for general business and departmental use. It was sold alongside other product lines, each with a different architecture (System/3, System/32, System/34, System/36).

Realizing the importance of compatibility with the thousands of programs written in legacy code, IBM launched the AS/400 midrange computer line in 1988. AS stands for "Application System." Great effort was made during development of the AS/400 to enable programs written for the System/34 and System/36 to be moved to the AS/400. Programs on the System/38 were directly compatible with the new AS/400 (after they were 're-encapsulated' by the operating system).

In 2000, in accordance with IBM's eServer initiative, the AS/400 series was rebranded as the eServer iSeries. In 2006, it was again rebranded as the IBM System i. In 2008, almost 20 years after being introduced, the System i and IBM System p product lines were combined into a new product line called the IBM Power Systems line.[4]

The AS/400 operating system was originally named OS/400 (following the pattern begun with OS/360 and followed with OS/2). The operating system has undergone name changes along with the rebranding of IBM's server lineup. The operating system was rebranded as i5/OS to correspond with the introduction of POWER5 processors and the rebranding of the hardware to eServer iSeries. In 2008, the operating system was rebranded to IBM i, with the introduction of the IBM Power Systems.

The operating system is object-based. Features include a RDBMS (DB2/400), a menu-driven interface, support for multiple users, block-oriented terminal support (IBM 5250), and printers. IBM i has built-in security, and support for communications, and web-based applications which can be executed inside the optional IBM WebSphere Application Server or as PHP/MySQL applications inside a native port of the Apache web server.[5]

Unlike the "everything is a file" feature of Unix and its derivatives, on IBM i everything is an object (with built-in persistence and garbage collection). IBM i offers Unix-like file directories using the Integrated File System.[6] Java compatibility is implemented through a native port of the Java virtual machine.

Like IBM's mainframe operating systems, IBM i uses EBCDIC as the inherent encoding.[7]

OS/400 Version 4, Release 4 (V4R4) introduced LPARs (logical partitions) allowing multiple virtual systems to run on a single hardware footprint.


The IBM System i platform extended the System/38 architecture of an object-based system with an integrated DB2 relational database. Equally important are the virtual machine and single-level storage concepts which established the platform as an advanced business computer.

Instruction set[edit]

IBM AS/400e Model 150

One feature that has contributed to the longevity of the IBM System i platform is its high-level instruction set (called TIMI for "Technology Independent Machine Interface" by IBM), which allows application programs to take advantage of advances in hardware and software without recompilation. TIMI is a virtual instruction set independent of the underlying machine instruction set of the CPU. User-mode programs contain both TIMI instructions and the machine instructions of the CPU, thus ensuring hardware independence. This is conceptually somewhat similar to the virtual machine architecture of programming environments such as Java and .NET.

Unlike some other virtual-machine architectures in which the virtual instructions are interpreted at run time, TIMI instructions are never interpreted. They constitute an intermediate compile time step and are translated into the processor's instruction set as the final compilation step. The TIMI instructions are stored within the final program object, in addition to the executable machine instructions. This is how application objects compiled on one processor family (e.g., the original CISC AS/400 48-bit processors) could be moved to a new processor (e.g., PowerPC 64-bit) without re-compilation. An application saved from the older 48-bit platform can simply be restored onto the new 64-bit platform where the operating system discards the old machine instructions and re-translates the TIMI instructions into 64-bit instructions for the new processor.

The system's instruction set defines all pointers as 128-bit. This was the original design feature of the System/38 (S/38) in the mid 1970s planning for future use of faster processors, memory and an expanded address space. When at a point in the future 128-bit general purpose processors would appear, IBM i will already be fully 128-bit enabled. The original AS/400 CISC models used the same 48-bit address space as the S/38. The address space was expanded in 1995 when the RISC PowerPC RS64 64-bit CPU processor replaced the 48-bit CISC processor.

For 64-bit PowerPC processors, the virtual address resides in the rightmost 64 bits of a pointer while it was 48 bits in the S/38 and CISC AS/400. The 64-bit address space references main memory and disk as a single address set which is the single-level storage concept.


The IBM System i includes an operating system originally known as OS/400, later as i5/OS and IBM i. System i is also capable of supporting multiple instances of AIX, Linux, Lotus Domino, Microsoft Windows 2000 and Windows Server 2003. While OS/400, AIX, Linux and Lotus Domino are supported on the POWER processors, Windows is supported with either single-processor internal blade servers (IXS) or externally linked multiple-processor servers (IXA and iSCSI). iSCSI also provides support for attachment of IBM Bladecenters. Windows, Linux, and VMware ESX(VI3) are supported on iSCSI attached servers.

LPAR (Logical PARtitioning), a feature introduced from IBM's mainframe computers, facilitates running multiple operating systems simultaneously on one IBM System i unit. A system configured with LPAR can run various operating systems on separate partitions while ensuring that one OS cannot run over the memory or resources of another. Each LPAR is given a portion of system resources (memory, hard disk space, and CPU time) via a system of weights that determines where unused resources are allocated at any given time. The operating systems supported (and commonly used) under the LPAR scheme are IBM i, AIX, and Linux.

Other features include an integrated DB2 database management system, a menu-driven interface, multi-user support, non-programmable terminals (IBM 5250) and printers, security, communications, client–server and web-based applications. Much of the software necessary to run the IBM System i is included and integrated into the base operating system.

The IBM System i also supports common client–server systems such as ODBC and JDBC for accessing its database from client software such as Java, Microsoft .NET languages and others.


IBM AS/400 9404-B10 with a 5281 terminal

The IBM System i, then known as the AS/400, was the continuation of the System/38 database machine architecture (announced by IBM in October 1978 and delivered in August 1979). The AS/400 removed capability-based addressing.[1] The AS/400 added source compatibility with the System/36 combining the two primary computers manufactured by the IBM Rochester plant. The System/36 was IBM's most successful mini-computer but the architecture had reached its limit.

The first AS/400 systems (known by the development code names Silverlake, named for Silver Lake in downtown Rochester, Minnesota, where development of the system took place, and Olympic) were delivered in 1988 under the tag line "Best of Both Worlds" and the product line has been refreshed continually since then. The programmers who worked on OS/400, the operating system of the AS/400, did not have a UNIX background. Dr Frank Soltis, the chief architect, says that this is the main difference between this and any other operating system.

The AS/400 was one of the first general-purpose computer systems to attain a C2 security rating from the NSA (Gould UTX/C2, a UNIX-based system was branded in 1986[8]), and in 1995 was extended to employ a 64-bit processor and operating system.

The 1995 change-over from IMPI, with 48-bit addresses, to PowerAS, with 64-bit addresses, required that all programs be 'observable', i.e. that the debugging information had not been stripped out of the compiled code. This caused problems for those who had bought third-party products that had no source and no observability. In 2008, the release of i5/OS V6R1 (later known as IBM i 6.1) caused similar problems due to changes to the TIMI in that release.[9]

In 2000, IBM renamed the AS/400 to iSeries, as part of its e-Server branding initiative. At that time, it adopted more PC server-like features, such as PS/2 keyboards and mice and VGA video output, mostly coming from IBM PS/2 and Intel server line (called eServer xSeries), replacing proprietary technologies. In 2001, it switched to the POWER4 processor from the PowerAS processors used by previous generations.

The product line was further extended in 2004 with the introduction of the i5 servers, the first to use the IBM POWER5 processor. The architecture of the system allows for future implementation of 128-bit processors when they become available.

Although announced in 1988, the AS/400 remains IBM's most recent major architectural shift that was developed wholly internally. Since the arrival of Lou Gerstner in 1993, IBM has viewed such colossal internal developments as too risky. Instead, IBM now prefers to make key product strides through acquisition (e.g., the takeovers of Lotus Software and Rational Software) and to support the development of open standards, particularly Linux. After the departure of CEO John Akers in 1993, when IBM looked likely to be split up, Bill Gates commented that the only part of IBM that Microsoft would be interested in was the AS/400 division. (At the time, many of Microsoft's business and financial systems ran on the AS/400 platform, something that ceased to be the case around 1999, with the introduction of Windows 2000.[10][11][12])


The AS/400 was originally based on a custom IBM CISC CPU which had an instruction set architecture, known as Internal Microprogrammed Interface (IMPI), similar to that of the IBM System/370.[13] It was later migrated to a POWER-based RISC CPU family eventually known as RS64.[14]

CPU in AS/400, iSeries, i5, Power Systems[edit]

The System i5 used POWER CPUs, which were developed and manufactured by IBM. The POWER 4/5/5+ chips contain two cores. There are Multi-Chip Modules (MCM) available. They have 2 CPUs (4 cores) or 4 CPUs (8 cores) in one MCM.

CPU Year Clock Speed Server-Models
IMPI[note 1] 1988 > 22Mhz [note 2] Current stable version: AS/400 Bxx, Cxx, Dxx, Exx, Fxx, Pxx, 100, 135, 140, 2xx, 3xx[16]
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[17]
Pulsar (RS64 III) 1999 450 MHz Future release: iSeries;
System i
270, 820
IStar (RS64 III upgraded) 2000 400, 500, 540 or 600 MHz 820, 830, 840,[18] 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 GHz (2005)
1.9 GHz(2005)
2.2 GHz
2.3 GHz
i5-520, i5-550, i5-515, i5-525
POWER6 2007 3.5 GHz
4.2 GHz
4.7 GHz
BladeCenter JS12, JS22
i5-570 (MMA)
M50, M25 & M15
POWER6+ since 2009 3.6 GHz
3.8 GHz
4.0 GHz
4.2 GHz
4.4 GHz
5.0 GHz
BladeCenter JS12, JS22, JS23, JS43
Power 520, 550, 560, 570, 575, 595

Power Systems

POWER7 2010 3.3 GHz
3.6 GHz
3.7 GHz
4.2 GHz
BladeCenter PS700, PS701, PS702
PureSystems compute nodes p260, p460, p24L
PowerLinux 7R1, 7R2
Power 710, 720, 730, 740, 750, 755, 760, 770, 780, 795
POWER7+ 2012 3.7 GHz
4.2 GHz
4.4 GHz
BladeCenter PS703, PS704
PureSystems compute nodes p260, p460, p24L
PowerLinux 7R1, 7R2
Power 710, 720, 730, 740, 750, 755, 760, 770, 780, 795
POWER8 2014 2.5 GHz to 5.0 GHz Power S812L, S814, S822, S822L, S824, S824L, S812LC, S821LC, S822LC
Power E850, E870, E880
POWER9 2017 4 GHz Power AC922, L922, S914, S922, S924, H922, H924, E950, E980
  1. ^ There were at least two generations of IMPI processors, the second was released in 1991.[15]
  2. ^ "The processor clock cycle is 45ns worst case."[15]

Models of AS/400, iSeries, i5 systems[edit]

Model Year CPU Group 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, P20, P30 3,8 - 56,6
E02, E04, E06, E10, E20, E25, E35, E45, E50, E60, E70, E80, E90, E95 1992 P10, P20, P30, P40 4,5 - 116,6
F02, F04, F06, F10, F20, F25, F35, F45, F50, F60, F70, F80, F90, F95, F97 1993 P05, P10, P20, P30, P40 5,5 - 177,4
P01, P02, P03 1993-1995 P05 7,3 - 16,8
150 1996 P05 10,9 - 35,0
S10, S20, S30, S40 1997 P05, P10, P20, P30, P40, P50 45,4 - 4550
SB1, SB2, SB3 1997, 2000 P30, P40 1794 - 16500
10S, 100, 135, 140 1993-1995 P05, P10, P20 17,1 - 65,6
170 1998 P05, P10, P20 30 - 1090
200, 20S, 236 1994 P05, P10 7,3 - 17,1
250 2000 P05 50 - 75
270 2000 P05, P10, P20 50 - 2350
300, 30S, 310 1994 P10, P20, P30, P40 11,6 - 177,4
400, 40S, 436 1995 P05, P10 13,8 - 91,0
500, 50S, 510, 530, 53S 1995 P10, P20, P30, P40 18,7 - 650
600, 620, 640, 650 1997 P05, P10, P20, P30, P40, P50 22,7 - 4550
720 1999 P10, P20, P30 240 - 1600
730 1999 P20, P30, P40 560 - 2890
740 1999 P40, P50 3660 - 4550
800 2003 P05, P10 300 - 950
810 2003 P10, P20 750 - 2700
820 2000, 2001 P05, P10, P20, P30, P40 100 - 3700
825 2003 P30 3600 - 6600
830 2000, 2002 P20, P30, P40, P50 1850 - 7350
840 2000-2002 P40, P50 10000 - 20200
870 2002 P40, P50 7700 - 20000
890 2002 P50, P60 20000 - 37400
520 2004–2006 P05, P10, P20 500 - 7100
550 2004–2006 P20 3300 - 14000
570 2004–2006 P30, P40 3300 - 58500
595 2004–2006 P50, P60 24500 - 216000
515 2007 P05 3800 - 7100
525 2007 P10 3800 - 7100
570 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 2008
JS43 2008
570 (9117) 2008 P30 104800
595 (9119) 2008 P60 294700

See also[edit]

Preceded by
IBM RS/6000
IBM System p
2000 - 2008
eServer pSeries
eServer p5
System p5
System p
Succeeded by
IBM Power Systems
Preceded by
IBM AS/400
IBM System i
2000 - 2008
eServer iSeries
eServer i5
System i5
System i


  1. ^ a b Frank G. Soltis Fortress Rochester: The Inside Story of the IBM ISeries p.119
  2. ^ "IBM eServer iSeries 400". IBM. October 3, 2000.
  3. ^ Niccolai, James (April 2, 2008). "IBM merges System i and System p server lines". InfoWorld.
  4. ^ "System i users: Power Systems merger good, OS name change mixed".
  5. ^ "Zend Solutions for IBM i".
  6. ^ "File Integrity Monitoring for iSeries". Archived from the original on 2009-05-14.
  7. ^ IBMnt (2008). "IBM confirms the use of EBCDIC in their mainframes as a default practice". Archived from the original on 2013-01-03. Retrieved 2008-06-16.
  8. ^ "Gould, Inc. Computer Systems Division". Defense Technical Information Center. December 31, 1986.
  9. ^ Alex Woodie (2008-02-26). "i5/OS V6R1 Compatibility an Issue for Software Vendors". Retrieved 2021-03-16.
  10. ^ Microsoft TechNet. "AS/400s extinct at Microsoft since 1999". Google discussion group, Microsoft runs AS/400's in-house - Article?. Retrieved 2007-05-16.
  11. ^ "Disparition des systèmes AS/400 chez Microsoft depuis mai 1999". Archived from the original on 2012-11-06. Retrieved 2013-01-02.
  12. ^ "Microsoft Uses the iSeries to Run its Business". Blogspot,Confessions of An iSeries Priest. Retrieved 2006-03-05.
  13. ^ David McKenzie. "Notes for storage research". Archived from the original on October 8, 1999.
  14. ^ Soltis, Frank G. "When Is PowerPC Not PowerPC?". The 400 Squadron. Archived from the original on January 8, 2008.
  15. ^ a b Schmierer, Q.G.; Wottreng, A.H. (1991). IBM AS/400 processor architecture and design methodology. IEEE International Conference on Computer Design: VLSI in Computers and Processors. pp. 440–443. doi:10.1109/ICCD.1991.139942.
  16. ^ "AS/400e System Handbook" (PDF). IBM. 1999-08-03. Retrieved 2021-03-21.
  17. ^ "V4R3 Questions and Answers". Reference # 8625668200695613. Retrieved 2007-04-04.[permanent dead link]
  18. ^

External links[edit]