How to find the Tech Refresh (TR) level on AS400 / IBM iSeries

AS400 Operating System Introduction

So what makes the AS/400 Operating System so special?

The AS400 Operating System (or AS/400 System) is one of the most modern Operating Systems in widespread use today.  I was at an interesting talk by Doctor Frank Soltis the chief designer for the IBM AS/400 and the IBM System 38 that came before it. He explained that Windows can trace its roots back via Windows NT to VAX VMS, Unix, Linux and OSX can trace their roots back into the late 60’s. In comparison, OS/400 or CPF (Control Program Function) as it was known on the System/38 was designed from the ground up in the 1980’s.

In current terms, OS/400 has more in common with the Java Virtual Machine (JVM) than operating systems like Windows. OS/400 has a machine-independent layer that sits between it and the underlying processors and hardware.  

Over the years the processors on the AS400 System have changed many times, for example from CISC to RISC whilst marinating software compatibility. The software first compiled in the 1980s on long-forgotten hardware can still be run on the latest hardware today without being recompiled.

In addition to the Technology Independence Layer, OS/400 also features something called Single Level Storage.  In computer software, the most expensive operation is the Branch operation. This is where the processor switches from one task to another.  

OS/400 handles this by having a single continuous 128-bit address range. This covers all the physical memory and disk storage. The Operating System then uses hierarchical storage management to move the most frequently used content into the fastest memory in the single-level storage. These days this will range from slow mass storage drives, SANS, fast drives, SSDs to RAM.

OS/400 is not a truly Object Orientated Operating System in the current sense (i.e. inheritance and polymorphism) but it is Object-Based and very much embraces Encapsulation. Being an Object Based system literally everything on the system is an Object.

Each object has a set of interfaces and can only be accessed through those interfaces. This has made the platform incredibly secure as most of the memory overrun and buffer attacks that hackers exploit on other platforms are not possible.

The other interesting thing about OS/400 is that it has a built-in database. These days it’s called DB/2 and shares much of the DB/2 technology from other platforms. OS/400 uses this built-in database for many of its own storage requirements. DB/2 on iSeries leverages the single-level storage to be highly reliable and low maintenance.  

Unlike on other platforms the AS/400 will run for years without any operator or DBA (Database Administrator) assistance.  For example, I’m aware of several companies in the UK where AS/400 applications run for years on end with little to no operations support.

I’d contrast this with Microsoft SQL Server-based applications where performance degrades if not given regular attention.  IBM S/38 was the first commercial computer to implement a Relational Database using SQL. This took the conceptual work from Ted Codd at IBM and implemented it for real in the S/38.  

At the time the S/38 CPF Operating System was ahead of the processing power available for this type of processing. It was slow but successfully proved the vision of a Relational Database based on SQL. IBM had invested everything in the development of the S/38 and continued this investment as they improved the processors, hardware and Operating System and relaunched it in the 1990s as AS/400.

The AS/400 as a whole is often perceived to be out of date (by people who don’t know better) because it still runs many Green Screen or Character-based applications on dumb terminals or terminal emulation.  From a systems architecture perspective, this is no more relevant than say the console interface on Mac OS (OSX) or the Terminal Interface on Windows.

These days most modern applications are browser-based and the users would never know that the backend is running on OS/400.

For anyone studying Systems Architecture or Computer Science OS/400, you must study to get an alternative view of how well a fully integrated, single-vendor system can work on an enterprise scale. Few doubt this today on the desktop or iPhone when they look at Apple products. To some extent, Microsoft Azure platform and Amazon’s AWS platform also seek to be a single vendor solution to all common business requirements.

What is AS400 used for?

AS400 is used for commercial applications such as manufacturing, warehouse management, stock control, Quote to Cash, Sales Order Processing and Purchase to Pay, and procurement applications. The AS400 is also a major platform in Banking and Insurance. The thing all these applications have in common is the need for highly available and accurate systems which are cost-effective and simple to operate.

You can very successfully run websites and web applications from the AS400 and it is certainly common to see the AS400 used as the backend transaction processing or system of record for critical web applications.

Is AS400 obsolete?

No, despite IBM’s frequent name changes the AS400, or IBM I (pronounced IBM EYE) is still a platform of choice for applications which require high levels of performance, confidentiality, availability and integrity in an easy-to-use and cost-effective single vendor package.

What kind of software is AS400?

Hopefully, the above article helps to explain that the AS400 is not software as such but is instead a computing platform. However, in many of the businesses I have worked in where the AS400 runs bespoke or custom applications, it is not uncommon to hear staff refer to the system as AS400. For example, people may say “We use the AS400 for order processing”. What they mean is their business runs a Sales Order Processing Application on an AS400-based system, these days most likely an IBM i.

What is the AS400 called now?

At the time of writing the latest name is IBM i (pronounced IBM EYE). IBM didn’t exactly help themselves by coming up with a name which isn’t so easy to Google. IBM had their reasons for the name change, but other key brands such as iPhone and PlayStation don’t feel the need to create a whole new name each time they update their technology to the next generation. If you are writing articles online I would strongly recommend that you include AS400 somewhere to help people find your content.

Is AS400 Unix based?

No, the AS400 or more precisely OS400 is not Unix-based. That said it does support the POSIX API and you can use the STRQSH command to get to a Unix-like command terminal. One of the reasons the name shifted from AS400 to IBM i is the fact that AS400 when it came out just ran one Operating System, whereas IBM i runs OS/400, Linux and IBM AIX. You can run all of these, and different versions of these at the same time in LPARS (Logical Partitions) and dynamically move resources between these.

For more information about POSIX please see, IEEE Standard Association. (2018). IEEE Std 1003.1™-2017 (Revision of IEEE Std 1003.1-2008), IEEE Standard for Information Technology—Portable Operating System Interface (POSIX®) Base Specifications, Issue 7. The Institute of Electrical and Electronics Engineers, Inc. Available at:

What is AS400 accounting software?

J D Edwards, owned by Oracle, and SAP are the two leading accounting packages on AS400. Many businesses continue to utilize software based on JBA’s Business. A distinctive feature of AS400 accounting software is its common practice of including source code. This empowers businesses to extensively customize off-the-shelf software, achieving a level of tailoring that often surpasses what is possible with cloud SaaS applications. My experience has shown that this customization is crucial. I have witnessed numerous migrations from AS400 to SaaS platforms struggle, mainly because the SaaS solutions fail to replicate the functionality and processing speed of the original AS400 applications.

Is AS400 an ERP system?

The AS400 is a computing platform which can run ERP (Enterprise Resource Planning) applications. It does this very well but it is not the only thing the AS400 can be used for. For example, in the UK the AS400 has been used for ticket sales at football grounds, where any outage on the day of a match could cause a serious health and safety issue. It is also used to drive the booking website for hotels and holiday parks where any downtime would become very expensive.

What language is AS400 software developed in?

The majority of the business applications on IBM AS400 (IBM i) are written in a version of RPG (Report Program Generator) a language IBM created many years ago to compete with and outperform COBOL. The system now supports a wide range of languages including Java, Python, PHP and C++.

What is XResize for DB2 and why do you need it?

Unlike newer applications like Salesforce, it is not always easy to add extra fields to AS/400 applications. More specifically, AS/400 applications rely on 5250 green screens and printed output. The programs can have database tables and data structure definitions stored internally. Also, the screens which are 80×24 or 132×24 have very limited space. Added to this the displays generally don’t dynamically adjust when new fields are added. Applications like xResize allow programmers to more efficiently determine the impact of adding a field or changing a field on the database. These applications can then make the change and leave the programmer to handle the exception.

It should be noted that many AS/400 applications do allow fields to be dynamically added by system administrators but like other platforms, this has to be designed into the applications when they are developed. It certainly gets easier when modern HTML-based user interfaces are involved.

How do I connect to an AS400 system?

To connect to an AS400 system, you generally use a terminal emulator like IBM i Access Client Solutions (ACS) or TN5250. These emulators provide a way to interact with the AS400 system remotely and can run on various platforms such as Windows, macOS, and Linux. It is also often possible to connect using a classic VT100 terminal emulation program, but if you do this it can be difficult to navigate the screens.

What are some popular AS400-based applications?

Some popular AS400-based applications include Infor LX, BPCS, MAPICS, and PRMS. These applications cater to different industries and business processes, such as manufacturing, distribution, and finance.

How do I learn AS400 programming?

To learn AS400 programming, you can start by studying the basics of the RPG language, as well as other supported languages like COBOL, Java, Python, and PHP. You can find online resources, tutorials, and forums where experienced developers share their knowledge. Additionally, you can enrol in a formal course or attend workshops and seminars that focus on AS400 programming.

How secure is the AS400 platform?

The AS400 platform is known for its security features, which include object-level security, encryption, and system auditing. These features help protect data and applications from unauthorized access and tampering. Additionally, the object-based nature of OS/400 makes it less susceptible to common security vulnerabilities, such as buffer overflows and memory corruption.

How does the AS400 compare to other platforms in terms of cost and performance?

The AS400 is known for its reliability, high performance, and low maintenance costs. While the initial investment for an AS400 system might be higher than other platforms, its total cost of ownership can be lower due to reduced downtime, simplified management, and minimal need for ongoing administrative support. Additionally, AS400 systems are scalable and can handle large workloads, making them an attractive option for enterprises with mission-critical applications.

How can I migrate my AS400 applications to a modern platform?

Migrating AS400 applications to a modern platform can be a complex process, as it may involve rewriting code, redesigning user interfaces, and adapting data structures. It is essential to perform a thorough analysis of the existing application, identify potential challenges, and plan the migration process accordingly. Some organizations may choose to retain some AS400 functionality while integrating it with modern technologies like web services and cloud-based applications.

Where can I learn more about AS400?

Official Documentation and Resources: As the developer of AS400, IBM’s official documentation, product guides, and whitepapers are primary sources of authoritative information.
IBM Knowledge Center: IBM i Documentation
IBM Redbooks: IBM Redbooks on AS400/iSeries These deep dive guides show how to use various IBM and AS400 services to create powerful solutions and solve problems.

How to find which version of OS/400 & IBM i you have installed?

AS/400 Command cheat sheet

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1 Comment
  1. Abdul Shakoor

    Very impressive and interesting

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