IBM AS400 - Historical Journey and Future

Gaurav Kumar | September 14, 2022


Historical Journey

It’s been 47 years since System/38 was launched and the journey continues with the recently released cloud-based IBM-i Merlin (Modernization Engine for Lifecycle Integration).

Family of Midrange Computers

The IBM AS/400 (Application System/400) is a family of midrange computers from IBM. Midrange computers, or midrange systems, is a class of computer systems that fall in between mainframes computer and microcomputers. Here’s a brief timeline of IBM’s midrange systems that eventually led to the AS400 Family.

Year Name Details First In Pictures
1969 System/3 It was the first IBM midrange system Picture2-Sep-14-2022-10-09-35-64-PM
1975 System/32 It was a 16-bit single-user system also known as the IBM 5320 Picture3-Sep-14-2022-10-10-43-69-PM
1977 System/34 It was intended as a successor to both the System/3 and System/32. Picture4-Sep-14-2022-10-15-10-86-PM
1978 System/38 It was the first Midrange system to have an integrated relational database management system (DBMS). The S/38 had 48-bit addressing and ran the CPF (Control Program Facility) operating system. Picture5-Sep-14-2022-10-15-47-22-PM
1983 System/36 It had two 16-bit processors with an operating system that supported multitasking. Picture6-Sep-14-2022-10-16-19-51-PM
1988 AS/400 It was introduced in 1988, renamed eServer iSeries in 2000, and subsequently became IBM System i in 2006. It ran the OS/400 operating system. Picture7-Sep-14-2022-10-20-47-09-PM
2008 IBM Power Systems Popularly Known as IBMi Power Systems is a family of server computers from IBM that are based on its Power processors. It was created in 2008 as a merger of the System p and System i product lines. Picture8-Sep-14-2022-10-21-02-80-PM


IBM AS/400

As a member of the Midrange computers lineup from IBM, AS/400 was released in 1988, and ran the OS/400 operating system. Lower cost but more powerful than its predecessors, the AS/400 was extremely successful at launch, with an estimated 111,000 installed by the end of 1990 and the associated revenue reaching $14 billion that year.

It is one of the most secure, stable, reliable, and scalable platform for web & mobile business applications.

The AS/400 architecture inherits several principles from System/38

System Architecture of IBM AS/400

AS/400's architecture is defined by five architectural principles:

  1. Technology Independence: A key concept in the AS/400 platform is Technology Independent Machine Interface (TIMI), a platform-independent instruction set architecture (ISA) that is compiled along with the native machine language instructions. The platform has used this capability to change the underlying processor architecture without breaking application compatibility.
  2. Software integration: OS/400 (now known as IBM i) is the native operating system of the AS/400 platform, and was the sole operating system supported on the original AS/400 hardware. Many of the advanced features associated with the AS/400 are implemented in the operating system as opposed to the underlying hardware, which changed significantly throughout the life of the AS/400 platform. Features include a RDBMS (Db2 for i), a menu-driven interface, support for multiple users, block-oriented terminal support (IBM 5250), and printers.
  3. Object-based design: On IBM I, everything is an object be it a Printer Device, Programs, Web Services, APIs, Programs, Files, etc.
  4. Single-Level Store: The term originally referred to what is now usually called virtual memory. So, the term Single-Level store is a computer storage term which has had two meanings. The two meanings are related in that in both, pages of memory may be in primary storage (RAM) or in secondary storage (disk), and that the physical location of a page is unimportant to a process.
  5. Hardware Integration: Later generations of hardware are also capable of supporting various guest operating systems, including SSP, AIX, Linux, Microsoft Windows 2000 and Windows Server 2003. While OS/400, AIX, and Linux are supported on the POWER processors on LPARs (logical partitions), Windows is supported with either single-processor internal blade servers (IXS) or externally linked multiple-processor servers (IXA and iSCSI). SSP guests were supported using emulation from OS/400 V3R6 through V4R4 using the Advanced 36 Machine facility of the operating system, a feature distinct from the System/36 Environment compatibility layer which requires System/36 software to be recompiled.




It was originally released in 1988 as OS/400, as the sole operating system of the IBM AS/400 line of systems. It was renamed to i5/OS in 2004, before being renamed a second time to IBM i in 2008. The two most recent versions of the operating system at that time, which had been released as i5/OS V5R4 and V6R1, were renamed to IBM i 5.4 and 6.1

IBM i Architecture


Features of IBM i Architecture

The first language supported by this system was RPG and then the subsequent versions of RPG followed as the system evolved. It now comes in various sets like RPG IV, OVM and ILE, with the following features:

  1. Database Management: IBM i features an integrated relational database currently known as IBM Db2 for IBM i. A storage engine for MySQL and MariaDB named IBMDB2I allows applications designed for those databases to use Db2 for i as a backing store. Other open-source databases have been ported to IBM i, including PostgreSQL, MongoDB , and Redis.
  2. Networking: IBM i supports TCP/IP networking in addition to the proprietary IBM Systems Network Architecture. IBM i systems were historically accessed and managed through IBM 5250 terminals attached to the system with twinax cabling. With the decline of dedicated terminal hardware, modern IBM i systems are typically accessed through 5250 terminal emulators. IBM provides two terminal emulator products for IBMi
    1. IBM i Access Client Solutions is a Java-based client that runs on Linux, macOS, and Windows provides 5250 emulations.
    2. IBM i Access for Web/Mobile provides web-based 5250 emulations.
      In addition, IBM provides a web-based management console and performance analysis product named IBM Navigator for i.
  3. Open-Source: Some of the ported open sources are, Apache HTTP, Node.js, gcc, Python, R, Perl, PostgreSQL Server, OpenSSL, nginx, Ruby, MariaDB, Redis, Vim, Java, Git, PHP, Lua, MySQL, MongoDB
  4. Programming: It includes RPG, Control Language, C, C++, Java, EGL, COBOL, and REXX. The Integrated Language Environment (ILE) allows programs from ILE-compatible languages (C, C++, COBOL, RPG, and CL), to be bound into the same executable and call procedures written in any of the other ILE languages.
    Certain development tools for IBM i run on top of the operating system itself, such as the Source Edit Utility (SEU) text editor and Programming Development Manager. IBM also provides an Eclipse-based integrated development environment (IDE) for IBM i named IBM Rational Developer for i which runs on developer workstations instead of IBM i. Prior to the Eclipse-based IDE, IBM provided an IDE based on WorkFrame/2 which ran on OS/2 named CODE/400 and an IDE based on VisualAge which ran on Microsoft Windows systems.
    IBM i uses EBCDIC as the default character encoding, but also provides support for ASCII, UCS-2 and UTF-16
  5. Storage: In IBM i, disk drives may be grouped into an auxiliary storage pool (ASP) in order to organize data to limit the impact of storage-device failures and to reduce recovery time
  6. Security: To date it is the only hack-free system. Security in IBM i is defined in terms of authorities, which represents the permission to carry out a specific action on a specific object. Authorities can be granted to individual users (known as user profiles), groups (known as group profiles) or all users (public authorities). Security levels range from level 10 to level 50.

Below are a few important releases on IBM i:


Future of IBM I – MERLIN

Cloud was added to the latest release called MERLIN (“Modernization Engine foR Lifecycle IntegratioN”). Merlin is a set of tools that run in OpenShift containers which guide and assist software developers in the modernization of IBM i applications, allowing them to realize the value of a hybrid cloud, with multi-platform DevOps implementation.





Thousands of companies across verticals like banking, healthcare, insurance, retail & manufacturing use AS400.

Given such vast adoption, I believe that the future is bright IBM i programmers. The introduction of Merlin positions the platform for future innovations.


  1. Document References:
    1. IBM AS/400 - Wikipedia
    2. IBM i - Wikipedia
    3. IBM i Modernization Engine for Lifecycle Integration (Merlin) Overview
    4. IBM i Modernization Engine for Lifecycle Integration | IBM
  2. Technical References (Docs and Blogs) for learning IBMi:
    1. IBM i PDF files and manuals - IBM Documentation
    3. RPGPGM.COM - From AS400 to IBM i
    4. Scott Klement's web page
  3. Technical Groups for AS400:
    1. ILE - RPG Developers (RPGLANGUAGE) - | Groups | LinkedIn
    2. IBM i, iSeries, and AS/400 Professionals | Groups | LinkedIn

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