What is AS400 Operating System?

AS400 Operating System is a series of mid-range server operating systems developed by IBM and it’s also known as OS400. It is made to give businesses computing solutions that are secure, reliable, and very cost-effective. The AS400 Operating System (OS/400) family of computers has been around since 1988 and is still used by many organizations today.

AS400 Operating System
AS400 Operating System

What is AS400 Operating System?

AS400 Operating System is a type of system software that runs on IBM mid-range computers. It provides the necessary services for users to access and use their applications or programs, such as resource management and communication. OS/400 also comes with an integrated suite of applications and tools, allowing businesses to manage their data and operations from one platform easily.

Companies seeking to streamline their ERP processes can benefit immensely from the AS400 Operating System. By integrating planning, inventory management, and sales/marketing/finance operations into a single platform, businesses gain huge efficiency and time savings – making this OS a must-have for any enterprise looking to stay ahead of the competition.

How to use AS400 Operating System

AS400 was divided into two distinct sections:  SLIC and Extended Control Program Facility (XPF), both of which were managed by the Technology Independent Machine Interface (TIMI). TIMI served as a hardware abstraction layer, meaning users can execute an operating system and application software on different machines without recompiling.

Explore AS400 with IBM’s 1959 RPG programming language. Here’s a tutorial to help you get started on mastering this intricate system.

Upon booting up your machine, the AS400 system will display a Menu with tailored options based on your computer settings. Directly beneath is the command line where you can type in instructions for the program to decipher and act upon. Following this comes Function Keys – shortcuts enabling quick access to functions such as F3-exit, F4-prompt, and F12-cancel. Finally, an information area below displays updates based on current activity.

Simplify your navigation experience with the GO command tutorial! Simply type “go” on the command line, followed by whichever menu you need to access for a streamlined user journey. Enjoy a faster performance in no time at all! To access the program menu, simply type “go program,” and you’ll be presented with a list of options. Want to use numbers instead? No problem! You can quickly navigate through menus by entering the corresponding number on the command line. Alternatively, you can even just enter the title of your desired Menu option – it’s that easy! Plus, if something goes wrong or changes your mind during any process mentioned above, pressing F12 will allow you to cancel what was selected and take you back to the main menu.

To remove, change or re-number your menu options in the AS400 system: First, click on the option number and replace it with a zero (0). Then, place your cursor right after the option number and switch to your desired figure. Finally, if you wish to re-number all of them at once, press F4 – doing so will complete this process automatically.

AS400 Operating Systems

The architecture of the AS400 Operating System

IBM I was originally marketed as AS400 with two layers: the hardware-dependent System Licensed Internal Code (SLIC) and the hardware-independent Extended Control Program Facility (ECPF) (XPF). TIMI hardwires these components. Later versions included Portable Application Solutions Environment (previously Private Address Space Environment), which added AIX compatibility, and Advanced 36 Machine environment for System/36 SSP applications in emulation. AS400 has layers like:


TIMI goes above and beyond traditional operating systems by isolating users and applications from the underlying hardware. It abstracts the processor’s instruction set architecture, address space size, I/O, and persistence specifics. TIMI relies on two interconnected mechanisms to achieve this result: a Hardware Abstraction Layer (HAL) for virtualizing the base hardware and a Machine Interface (MI), which provides a unified logical view of the system to both users and programs.


The IBM Power architecture generates the SLIC, translating TIMI instructions into machine code and enabling particular features like an integrated relational database in As400. The System Storage Integrator (SLIC) V3R6 release lets system storage for IBM i with any operating system. Merging the single-level store addressing scheme and object-based storage model from IBM i can lead to several issues.


The Extended Control Program Facility (XPF) is a paramount part of the AS400 operating system, offering tools and services for application creation, data access, and system administration. Its primary introduction was AS/400 V21R0M0 as an assembly of APIs to create device drivers. As the XPF evolved, it eventually encompassed a suite of application development tools, data access services, and system management functionalities. Given that both the XPF and SLIC are written in the POWER assembly language, they have become closely woven into the operating system’s inner workings.

Portable Application Solutions Environment (PASE)

In May 2001, IBM enabled businesses to reap the advantages of their existing AIX applications by introducing PASE – A portable Application Solutions Environment. This set of tools and libraries allows businesses to run 32-bit and 64-bit AIX applications on AS400 servers with just a few clicks. Not only that, but it also gives them the power to leverage Linux apps on IBM i too! With this incredible technology, companies can easily move all their data into one platform without hassle or compatibility issues – making life easier for everyone involved.

Read also: What is AS400 ERP Software? AS400 Accounting Software

Database management in AS400 Operating System

Modified from its non-relational System/38 forerunner, the AS400’s IBM Db2 for IBM I offers a powerful integrated relational database. Boasting support of the SQL language and relational model, this system was aptly dubbed “database support” during its inception.

The AS400 offers two options to link to the integrated database – System/38-style native interface and SQL. The low-level Database Requestor (DBR) APIs are incorporated in the native interface, while SQL, a high-level declarative language, is easier for application development. While DBR allows access to data, its complexity makes it inappropriate for creating applications, whereas working with SQL is considerably simpler and better suited for such tasks.

Application Development in AS 400 operating system

The AS 400 provides developers with the powerful Integrated Application Development Environment (IADE) – a graphical development platform that can be utilized on Windows, Linux, and macOS. This software is packed with numerous tools to assist in creating user interfaces, applications, and databases quickly & effortlessly.

Leverage the Eclipse platform to access IBM i-specific resources with IADE’s plugins. Developers can call system APIs and structurally manage database objects with these helpful tools.

Storage & Security in AS400 Operating Systems

AS400 servers come standard with a generous 250 GB of storage, while As400 can store even more data at 500 GB. For larger businesses looking for an enterprise-level solution, AS400 offers up to 16 TB of available memory space, and As400 scales up to 32 TB.

AS400 has many security features, including role-based access control and object-level security. The As400 server also provides secure user authentication, encryption, digital signing of application data, and an integrated audit trail for tracking system changes. All these features make As400 a secure platform for running business applications.

Hardware integration & Technology Independence in AS400 Operating System

Leveraging AS400 servers to their fullest potential is easy with the many integrated hardware options available, such as storage controllers and network adapters. This allows for maximum technology independence and easy integration with existing systems. AS400 also includes several software options, such as HMC (Hardware Management Console), to monitor and manage the server’s hardware components.

If you’re a small business looking for reliable and independent computing power, then AS400 is the perfect solution. Based on IBM’s Power platform, AS400 can run any server that runs on this system while remaining highly autonomous. With its impressive capabilities and no need for expansion plans, AS400 is well worth considering as an invaluable addition to your business.

Networking in AS400 Operating Systems

AS400 takes networking to the next level with support for multiple protocols and virtual networks. But that’s not all – it also provides hardware-based encryption, which helps ensure proper security for each network connection. With AS400, you can rest assured knowing your data is in good hands!

The AS400 operating system also includes a comprehensive suite of resource management tools. This consists of an integrated security framework, which provides access control for all connected devices in the network. Additionally, it supports advanced routing protocols and other features that enable users to customize their network configurations according to their needs.

Frequently asked questions

Is AS400 an operating system?

The current operating system used on the Power platform is IBM i. Os400, an obsolete version of AS400 systems, was utilized in previous versions of the technology. As400 is currently used for all AS400 machines and isn’t compatible with Os400. Therefore, if you have a legacy Os 400 system installed, upgrading to As 400 will enable compatibility with today AS 400 platforms.

IBM Power Systems have long relied on AS400 as the primary operating system. Initially launched in 1988, it was renamed i5/OS just 16 years later and again dubbed IBM I in 2008. Every reliable update of this computer OS has proven its unparalleled power over other systems available today. With a System/38 CPF operating system as its base, the Machine Interface and object-based addressing on top of a single-level store are features imported from the System/38 platform. Furthermore, this powerful technology offers compatibility layers for System/36 SSP and AIX applications and tight integration with an incredibly efficient relational database into the OS.

What is the AS400 operating system used for?

AS/400 architecture is renowned for its dependability and has been selected by several industries that need enormous stability, such as manufacturing. IBM Power Systems are widely popular with SAP users but also work optimally with Oracle Database and other database management systems.


The IBM AS400 Operating System is an ideal choice for businesses looking for an enterprise-level computing platform that offers reliability, scalability, security & flexibility. Its comprehensive features and robust architecture make it well suited to tackle today’s data-intensive applications. Additionally, its support for multiple platforms makes it an excellent choice for cross-platform development projects. Therefore, AS400 remains one of the top enterprises looking for reliable yet cost effective solutions.

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