Have you heard of the OS/400 operating system from IBM? If you‘re not an enterprise computing historian, I wouldn‘t be surprised if the answer is no!
But for thousands of organizations worldwide running IBM Power Systems, OS/400 isn‘t just some legacy software – it‘s the foundation that‘s reliably powered their mission-critical business applications for over 30 years!
So in this guide article, I want to walk you through exactly what OS/400 is, why it mattered so much in its heyday, and how it continues impacting systems still running today…
Overview: The Integrated Business OS for IBM Minicomputers
At its core, OS/400 was an operating system released by IBM in 1988 specifically to run on their midrange AS/400 minicomputers. The "400" designation in the name refers to the series it was designed for.
OS/400‘s purpose was to handle complete integrated business workloads – everything from databases, reporting, ERP software, inventory programs etc. – without needing other computers or add-ons. This turned pricey IBM minicomputers into "do it all" business systems for medium sized organizations.
To enable this end-to-end business functionality, OS/400 had to be robust and user-friendly despite limited hardware resources. So IBM made two revolutionary architectural decisions…
First – abstract the underlying hardware complexity away to prevent replacing computers from breaking software.
Second – utilize a simplified "single level" storage model instead of complex file hierarchies. That provided resilience without high administration overheads.
These innovations came straight from the mind of legendary IBM inventor Frank Soltis…
The Brilliant IBM Scientist Who Invented OS/400
In many ways, OS/400 traces its lineage directly back to chief architect Frank G. Soltis – an American IBM computer scientist who led development of the AS/400 system software and hardware.
Frank G. Soltis – Image from Wikimedia Commons
Soltis made his name evolving IBM‘s System/3 line of servers into successors like System/36 and System/38 – but these incremental upgrades had limitations…
You couldn‘t abstract the system software from hardware dependencies. That forced application rewrites with every new generation of machine.
So for the AS/400 and OS/400, Soltis took a clean sheet approach. His key innovations like TIMI and single level storage delivered generational compatibility unheard of from competing vendors.
Let‘s unpack how Frank achieved that!
Soltis‘s Hardware Abstraction Innovation = TIMI
The magic ingredient allowing OS/400‘s longevity was something Soltis created called TIMI – Technology Independent Machine Interface.
This was a layer separating all system hardware dependencies from higher level software. It meant Components like storage controllers, processor architecture etc could change without impacting applications!
Here‘s a diagram showing how TIMI provided this insulating abstraction:
| Hardware | TIMI | OS/400 | Apps |
|---|---|---|---|
| System Drivers | Abstraction Barrier | Machine Services | Programming Interfaces |
| Controllers | Storage Management | Application Logic | |
| Processor Units | Task Scheduling | User Workloads |
By dividing hardware from software, Soltis future-proofed OS/400. Companies could start with an AS/400 running specialized programs…then continuously replace it with better Power System machines without software rewrites!
Soltis‘s Storage Breakthrough = Single Level Memory
Alongside hardware abstraction, Soltis introduced another pivotal innovation: single level storage.
Traditional systems utilize layered memory models – separate locations for user data, OS files, etc. But single level storage eliminates divisions between disk, memory, caches and registers – unifying everything into oneflatten hierarchy.
In practical terms, this meant OS/400 could shift data around dynamically as needed while programmers accessed everything through the same interface. There were no separate "drives" to manage.
By simplifying storage infrastructure, Soltis made OS/400 effortless to scale and administer long-term relative to Unix boxes – helping justify IBM‘s typically higher initial server costs for businesses.
These concepts help explain why OS/400 gained such loyalty among enterprises running IBM minicomputers…
OS/400 vs Unix – Night & Day System Software Architectures
Under the covers, OS/400 and Unix take completely different approaches:
| Area | OS/400 | Unix |
|---|---|---|
| Storage | Single-level | Hierarchical directories |
| Hardware | TIMI abstraction | Kernel & drivers |
| Language | RPG | C programming |
| Database | Integrated DBMS | Relational databases |
The Unix filesystem is far more nimble and customizable – but also complex to setup. OS/400 traded flexibility for resilience and ease-of-use – crucial for mission-critical business systems.
These opposing priorities characterized the platforms:
- Unix servers excelling at flexible application development
- IBM minicomputers built for resilient business processing
And over 3 decades, IBM kept extending OS/400‘s capabilities…
The Incremental Evolution of OS/400 1988 – 2008
Over a 20 year lifespan, IBM continued enhancing OS/400 across hardware refreshes:
| Release | Year | Major New Features |
|---|---|---|
| V1R1 | 1988 | Initial OS/400 |
| V2R1 | 1991 | Documentation Tools |
| V3R6 | 1995 | Monitoring/Admin |
| V4R4 | 1999 | Backups & Security |
| V5R3 | 2004 | Scheduling Engine |
| V6R1 | 2008 | Final i5/OS – Unicode Support |
Notice that between V5R3 and V6R1, the naming switched from OS/400 to i5/OS!
By the mid 2000s, IBM rebranded their AS/400 line as "System i" – thus the OS got a corresponding rename.
But this was mostly surface level – underneath i5/OS retained nearly full compatibility with old OS/400 releases. That meant minimal disruption for established customers. Apps and databases largely carried forward.
Here was the double-edged sword though…
Lasting Legacy vs. Eventual Limitations
Clearly companies enjoyed incredible investment protection running OS/400 for 20+ years without rewriting applications!
However the extreme backwards compatibility also hampered IBM from more radical hardware and architectural modernization. Any shifts had to be incremental to avoid breaking business critical software relying on very old OS foundations.
By the 2010s, rival Intel servers offered cheaper alternatives updated much faster than IBM‘s pace. Open source Linux gained favor over OS/400‘s proprietary environment as well.
These challenges of commoditization pressured IBM‘s whole minicomputer segment. Something had to give.
So as we‘ll see, OS/400 has now taken on more specialized niche duty for IBM…
OS/400 Today: The IBM I & Legacy Modernization
Around 2008, IBM made their "Flex System" initiative official. This ended OS/400‘s long standing general purpose OS tenure by:
Rebasing servers on fully commodity hardware and Linux
Launching IBM i – a modernization layer atop OS/400
IBM i delivers old OS/400 benefits like RPG compatibility and data resilience PLUS modern interfaces and toolchains. This balances legacy and openness; specialty capability and flexibility.
Now in 2022, IBM i sees gradual migrations of longtime OS/400 users desiring updated integration and features while preserving in-house software investments.
Companies less concerned about backwards compatibility can now choose commodity IBM servers and Linux instead – reducing costs. Meanwhile longtime AS/400 firms get a middle road to slow modernization through IBM i preserving their niche capabilities.
It‘s the best way to balance between far extremes – neither OS abandonment nor total antiquation. This careful stewardship of 40 years of IBM midrange innovations remains OS/400‘s lasting gift to enterprise computing!
So while the OS/400 name itself recedes into history, its technological DNA and the needs it serviced live on in every new IBM Power System deployment keeping key processes flowing via IBM i without a blip!
Conclusion: The OS/400 Legacy Survives Through IBM i
I hope this guide has shed light on OS/400‘s relevance past and present. What began in 1988 as the integrated business OS for AS/400 minicomputers remains the trusted foundation beneath thousands of productive IBM i installations today.
By pioneering timeless innovations like Frank Soltis’ TIMI abstraction to insulate software from underlying hardware changes, OS/400 delivered generational compatibility and day-in, day-out reliability rival vendors still struggle to match.
Yes – limitations of excessive backward looking focus have pushed OS/400 specifically into retirement. But the IBM i platform continues leveraging its bedrock principles modernized for the 2020s. And that means the OS/400 legacy proudly persists in every new Power server deployed – 3+ decades and counting!
So next time you hear about a company still reliant on old green-screen apps and proprietary databases, remember the story behind that resilience! OS/400’s specialsauce gave IBM midrange platforms easy lock-in for better and worse. But thanks to balanced modern meldings like IBM i, the programming language and unique capabilities conceived decades ago look poised to survive long into the cloud native future – smarter, faster and more platform agnostic than ever before!
