IBM’s AS/400 series, originally introduced in 1988, has been a pivotal player in the world of midrange computing for decades. Over time, this series evolved, eventually being rebranded as the IBM iSeries, and later as IBM Power Systems.

In this blog, we’ll delve into the history of IBM’s midrange computing offerings, comparing the AS/400 series to its successors.

AS/400 Series

The AS/400 series, short for “Application System/400,” was a groundbreaking line of computers designed for midsize businesses and enterprises.

This series represented a significant departure from IBM’s previous midrange systems, offering a combination of hardware and software innovations that simplified administration and made application development more accessible. Key features of the AS/400 series included:

  1. Integrated Architecture: The AS400 series was known for its integrated architecture, which combined powerful processor, storage, and database capabilities in a single system. This streamlined approach simplified system management and maintenance.
  2. Single-Level Store: AS/400 introduced a unique single-level store, where both program code and data were stored together. This design choice simplified data access and management, reducing the complexity of traditional file systems.
  3. Security: Security was a top priority in AS/400 systems, with built-in features such as object-level security and role-based access control. This made it an attractive choice for businesses with strict security requirements.
  4. Programming EnvironmentAS400 introduced the Integrated Language Environment (ILE), which allowed developers to use multiple programming languages, including RPG, COBOL, and C, within the same application.
  5. High AvailabilityAS400 systems were renowned for their high availability features, including hardware redundancy and data mirroring, ensuring minimal downtime for critical business applications.

IBM iSeries

In 2000, IBM rebranded the AS/400 series as the IBM iSeries. This rebranding came with improvements and updates to the hardware and software while retaining the core AS/400 principles. Key advancements during the iSeries era included:

  1. Increased Performance: The iSeries brought significant performance enhancements, thanks to faster processors and expanded memory capabilities, allowing businesses to run more demanding applications.
  2. Partitioning: The introduction of logical partitioning (LPAR) allowed users to run multiple virtual servers on a single physical machine, enhancing resource utilization and cost efficiency.
  3. Linux Support: IBM began offering support for the Linux operating system on iSeries servers, opening up new possibilities for running a broader range of applications.


The evolution of IBM’s midrange computing offerings from the AS/400 series to IBM Power Systems has been marked by a commitment to integration, security, performance, and adaptability. While the names and technologies have evolved, the core principles of simplicity, reliability, and scalability have remained constant.

Today, IBM Power Systems continues to serve as a robust and flexible platform for businesses of all sizes, maintaining the legacy of the AS/400 series that revolutionized midrange computing over three decades ago.