What Is AS400? Key Features, History, and Business Applications

AS400 is IBM’s midrange business computing platform, originally introduced in 1988 to handle core operations like accounting, inventory, and manufacturing. Though the original hardware was discontinued, its technology lives on today as IBM i, running on modern Power Systems hardware.

For a platform introduced in the 80’s, it remains astonishingly relevant. Countless computer systems have come and gone over the years, but IBM’s creation refuses to fade into obscurity — organizations across finance, healthcare, retail, and logistics still rely on it for its reliability, security, and integrated architecture, handling essential functions from banking and inventory to full-scale manufacturing.

For those new to the AS400, you may wonder how it shaped the familiar work environment we know today, and how it became one of the most trusted business computing platforms. Here’s everything you need to know.

What Is AS400 Used For?

Introduced over 38 years ago, the AS400 is a line of midrange computer systems developed by IBM. It was designed specifically to handle day-to-day business operations and data.

The AS400 was highly popular because it integrated hardware, software, security, and data management capabilities. Not to mention how easy it was to use, with a simple UI, any small team can manage.

Some of the applications it supported include:

• Financial and accounting systems
• Inventory and warehouse management systems (WMS)
• Payroll processing
• Supply chain operations
• Enterprise resource planning (ERP)
• Manufacturing and production systems
• Other industry-specific solutions (retail, insurance, healthcare, etc.)

This was groundbreaking back in the day, when people and businesses still relied on paper and fax machines.

Desktop computers were only used by individual employees. On the other hand, an AS400 system supported multiple users, processed transactions, and stored valuable data.

It does all these key functions simultaneously with minimal downtime, saving companies time and money.

The Evolution of AS400 to IBM i

The AS400’s technology has gone through several upgrades over its long life.

People familiar with IBM products and history may still recognize the AS400, but it has since evolved significantly from its first iteration.

AS/400 Era (1988)

In the 70s and early 80s, network computers were practically exclusive to stockbrokers and sci-fi films. To run their businesses, companies relied heavily on System/36 and System/38 platforms.

When IBM released AS/400 in 1988, it combined the capabilities of its pioneering predecessors into a single convenient unit.

The first of the AS400 line featured the OS/400. The operating system came with built-in security, an integrated database, and backward compatibility.

The system delivered a remarkable performance, and demand skyrocketed immediately after release. Tens of thousands of units were sold within just two years, and small to medium-sized businesses adopted the AS400.

By 1997, IBM had already shipped half a million units outside the US.

In 1994, the tech company introduced the AS/400e, with “e” here meaning “e-business.” While still running on the same OS, the e variant supported Java, enabling businesses to access web-based applications.

iSeries and System i

It was not until 2000 that IBM decided it was high time to upgrade the AS/400, and the eServer iSeries was produced.

The rebranded computer system marked IBM’s growing interest in the internet-based business and e-commerce. It was a massive success, becoming the backbone for enterprise computing in the early 2000s.

The iSeries retained the same qualities that made the AS/400 a trusted platform. It was reliable, secure, and compatible with its older versions.

Some of the iSeries’ advantages include better scalability, Linux support, and web-based applications.

However, merely six years after the eServer iSeries, IBM renamed the platform again.

This time, they called it System i. The major upgrade is that it unified IBM’s Power Systems and improved visualizations.

IBM i on Power Systems

In April 2008, another massive overhaul to the AS400 happened when IBM merged its System p server lines with the System i into Power Systems.

At the same time, they changed the operating system from the IBM iSeries to the IBM i

IBM made the two lines share the same POWER architecture, which significantly reduced design and manufacturing costs. In addition to powerful processors, the security was enhanced and users can use the cloud.

Now, we’re at IBM Power Systems, modernized with cloud-native capabilities and integrated with modern technologies like AI and machine learning. Despite these changes, many IT professionals still refer to the platform as AS/400 today.

What is the difference between IBM i and AS400?

This is a common confusion for people new to IBM’s AS/400.

The difference between the IBM i and AS400 comes down to their nature. The AS400 is a type of computer system hardware, often referring to the original 1988 iteration.

On the other hand, the IBM i is a software, specifically an operating system, introduced in 2006. It’s the modern and rebranded name for the OS/400, which ran on the original AS400.

Today, when someone says “AS400,” they’re usually referring to the entire 1988 platform, which includes its hardware, operating systems, and applications.

The good news is that IBM has maintained exceptional backward compatibility, so older applications can still run on the current IBM i OS, requiring little or no modifications from the user.

How Does an AS400 System Work?

One of the primary reasons for this IBM system’s continued relevance is its unique architecture. Combining the OS, database, and security features in one place has made it a robust and versatile system.

IBM i Operating System

The IBM i OS (formerly OS/400) serves as the foundation of the AS400 and its latest iteration, the IBM Power Systems.

As an operating system, the IBM i can handle user access, workloads, memory allocation, hardware resources, and system operations.

One distinctive feature of the IBM i is its object-based architecture, which is a novel innovation of the AS400.

It treated everything, from files, data, devices, and programs, as “objects,” as opposed to “everything is a file” architecture.

It completely removed the need to manage file paths manually. Instead, IBM i handles the object location and access rights for the user.

Integrated Database (Db2 for i)

Many systems require you to install a separate database product to configure and secure independently.

IBM’s computer system, however, took a different approach and natively integrated built-in components, such as middleware, applications, and databases.

Unlike other operating systems, IBM i doesn’t require numerous third-party tools to function reliably, which simplifies administration and operations for businesses.

Despite this self-contained design, it still integrates seamlessly with external systems and technologies — including cloud platforms, mobile operating systems, and social media platforms.

Business Applications

Business applications are programs designed to perform specific tasks for an organization. These applications are either developed internally or purchased externally.

The AS400’s internal integration capabilities support customer relationship management (CRM), ERP, HRM, supply chain management, and enterprise systems.

It also accommodates other applications used in accounting, healthcare, and banking operations.

Security Framework

Watertight security has always been a hallmark of the AS/400 series.

What makes this possible is IBM’s decision to build security features directly into the system’s OS and not rely on add-on layers.

This is done through object-level security, an integrated DB2 database, hardware-enforced boundaries, and tightly controlled access mechanisms.

A user can’t simply open a directory and modify everything inside without explicit authority permissions.

The object-oriented design further tightens security, preventing users from inadvertently executing malicious files and making the architecture inherently resistant to typical malware.

Key Benefits of AS400

There are several good reasons why the AS400’s technology remains relevant after all these years. Some of its key benefits include:

• Integration: The integrated architecture is core to the technology. Although in the mid-range, the AS400 offers a complete solution by combining software, hardware, OS, and applications.
• Security: The already robust security means organizations in the finance, healthcare, and banking industries won’t necessarily need to invest in other protective features for sensitive data.
• Scalability: Another important benefit of the classic IBM computer is scalability. Businesses need to grow—and their systems with them. This makes the AS400 a great tool for organizations of all sizes.
• Compatibility: Applications developed decades ago can still run on today’s IBM hardware and OS with few modifications. This means older files, programs, and systems don’t quickly become obsolete with time.
• Cost-effective: The minimal administrative overhead of the AS400 stems from its object-based architecture, which doesn’t require a huge team of IT experts to maintain.

The system is also known for exceptional uptime and reliability, thanks to built-in redundancy and self-healing capabilities. It doesn’t require frequent reboots to update or manage its memory, allowing it to operate continuously with minimal disruption.

Why Is AS400 Still Used Today?

While the original AS400 was discontinued by IBM in 2013, the core technology remains in IBM i running on the IBM Power Systems hardware.

A major reason for its ever-remaining popularity is the many organizations worldwide that continue to rely on the AS400’s ability to handle their business operations.

In 2026, according to Land Base, over 900 organizations use IBM Power Systems, the majority of which are in the US. These companies include Amazon, Apple, Walmart, Target, Audi, Costco, and many more.

The platform continues to evolve with the business landscape, preserving compatibility with older applications while integrating with the new.

It remains stable and reliable. So, businesses that heavily invested in IBM Power Systems have little reason to switch.

Changing to a new environment would also mean rewriting their applications from scratch, migrating copious amounts of data, and retraining employees. The cost to do this makes it not worth it.

Common Misconceptions About AS400

There are several misconceptions about the AS400 (now IBM Power Systems) that persist. Here are some of them:

“IBM’s AS400 is Outdated”

While it’s true that the original 1988 AS400 hardware has been discontinued, its latest iteration, the IBM i, lives on and runs on the modern IBM Power Systems hardware.

The operating system continues to receive updates today and supports a wide range of contemporary enterprise needs.

“Green Screen Applications Only”

The misconception that the AS400 only supports green-screen applications likely stems from the fact that the technology was introduced decades ago.

This is untrue. In fact, many organizations, those that are hesitant to migrate to the cloud, have successfully integrated their IBM i systems with contemporary APIs, data analytics, and even AI tools.

“Nobody Develops AS400 Anymore”

The underlying architecture and operating system of the AS400 are still very much alive and being actively developed.

It has been renamed and rebranded by IBM over the years. But the platform, now the IBM i, has simply evolved to accommodate new technologies while retaining the qualities that made it an icon.

Industries That Commonly Use AS400

Industries that depend on reliable and secure computer systems to handle data and day-to-day transactions still use the AS400 technology.

Some of these users include:

• Insurance providers
• Retail and wholesale
• Government agencies
• Transport and logistics
• Healthcare providers
• Financial institutions

Many of these organizations process thousands, some even millions, of business transactions regularly.

They need a computer system that can operate consistently under a heavy, continuous workload, and the AS400 does exactly that.

AS400 Modernization

Modernization is a major concern for people who are on the fence about whether the AS400 is still worth the investment.

However, if your business operations require extreme reliability and highly secure data management without breaking the bank, the classic IBM technology is definitely worth considering.

Instead of abandoning the AS400 system, many choose to integrate it with new, helpful applications.

Today’s IBM Power Systems are more than capable of supporting APIs, web applications, cloud access, advanced analytics, and other functions critical to modern businesses.

Challenges Organizations Face with AS400

Despite its many advantages, organizations may still face a few challenges with AS400 environments.

A common problem for businesses is the lack of an IBM i professional. Many who have specialized in this particular computer system for decades are approaching retirement, so finding support could be difficult.

BCL Mainframe Services is among the few remaining providers experienced in hosting, managing, securing, and optimizing IBM i environments.

Another difficulty companies encounter is maintaining older applications that their teams have relied on for years. But this can be easily resolved with help from an IBM i expert.

How Managed AS400 Services Help Businesses

AS400/IBM i service providers can aid modern businesses in many ways.

They can help you monitor systems, optimize performance, update software, and set up backup and recovery protocols in case of disasters.

Partnering with a reliable team of AS400 support providers, like BCL, will reduce your operational risks while ensuring your environment is secure, compliant, and always available.

Don’t hesitate to reach out to BCL for all your AS400, IBM i, and mainframe needs!

FAQs

What does AS400 stand for?

IBM’s AS400 stands for Application System/400. It has long been rebranded to IBM Power Systems, while retaining many of the core ecosystem’s features.

Is AS400 the same as IBM i series?

While often used interchangeably, the AS400 and IBM i series aren’t precisely the same. The IBM i is the modern OS that evolved from the original OS/400.

Is AS400 still supported by IBM?

Yes, the AS400’s core platform (now IBM i) is still supported by IBM, despite the original hardware being retired.

What programming languages are used on AS400?

Many AS400 applications are written in RPG, COBOL, SQL, and CL. Modern environments may use Java, Python, PHP, and other modern languages.

What is the difference between AS400 and a mainframe?

Both the AS400 and mainframe are enterprise computing platforms. The primary difference is their size and architecture, with a mainframe being designed for bigger transaction volumes.