Saturday, June 23, 2007


IBM's midrange workhorse

First of all, why should you care? The venerable AS/400 is three generations old. It was supplanted by the eServer iSeries in 2000. These upgrades have extended the useful life to the AS/400 platform. Consequently, there is still a large base of installed AS.400s. IBM estimates there are about 700,000 operational AS/400 systems all over the world.

Second, what can you expect? Practically all existing machines have newer Operating Systems and play new roles. They can be found acting as web servers, dedicated firewalls, database servers, application servers, and the like.

Finally, what’s the use of this overview? It will fill you in on the history and features of the AS/400 hardware. It’s useful for providing background information.

The AS/400 is the main system in the IBM midrange line. It was introduced in 1988 and is the continuation of the S/3x line. The latter began with the original S/3 (1969) and followed by the S/32, S/34, S/38, and S/36. Yes, the S/38 preceded the S/36. Collectively, these models are called the System/3x family.

The AS/400 systems offer more compatibility, portability, performance, expansion capability, and usability than the S/3x family.

Compatibility: Originally, only two operating systems ran on the AS/400. Today there are four: IBM® AIX®, IBM i5/OS®, and Linux® operating systems. This is also the first computer to use IBM’s Systems Application Architecture (SAA). This architecture allows application programs (“apps”) to be exchanged between different IBM models like the PS/2, S/3x, AS/400, and S/390s. This compatibility means that custom-written S/3x applications can be moved to the AS/400 without modification. In addition, the AS/400 can run apps written for IBM and non-IBM computers. This capability is referred to as portability.

Performance: The AS/400 is constantly being upgraded with faster processors, more efficient architectures, more storage, and improved disk units.

Expansion: The AS/400 family is fully compatible from its smallest to largest systems. Expansion towers for additional storage and more communication lines enhance the expansion capability of the family. Each system has expansion slots as well.

Usability: The regular OS is preloaded and its user interface conforms to IBM’s Common User Access (CUA) standard. This makes it consistent with other SAA environments, such as the OS/2 and PS/2.

AS/400s are multiuser machines. They are also application-centric systems. This means that it will execute and support an app and its data regardless of its origin (e.g., Windows, Macintosh, Unix, Java, etc.). This support may include network-centric systems. In this type, the apps and/or data may reside on separate systems, e.g., web servers. To repeat, an application-centric systems will run apps that were written for another vendor’s system.

AS/400s also support open systems, client-server, distributed, and host-centric computing.

Open systems do not just refer to Unix and Linux systems. Any operating system that are interoperable and portable are, by definition, open systems. Interoperability means that hardware and software from different vendors will work together. Portability refers to the capability to move apps, data, and users from one vendor or computer architecture to another. What are the benefits of open systems?

  1. Freedom of choice. The business is not limited to a specific vendor.
  2. Flexibility and change management over time. The business can recombine and redeploy their open systems apps and infrastructure as their needs dictate.
  3. Investment protection. New software and retraining is not required if the hardware platform is changed.

Client-server systems use workstations or desktops to access a server that holds the apps and data. The server provides the computation power and serves the clients with the results of their requests.

Distributed computing systems are similar to client-server systems. Instead of keeping a full copy of all the data and apps on the server, the data is segmented or partitioned and reside in various servers in the network.

Host-centric computing is the old computing platform paradigm. Users use dumb terminals for data interface. All computational capability resides in the host.

For more information, you may refer to these links:


The IBM eServer brand replaced the AS/400 family. The eServer brand has four lines:

The zSeries. This replaces the S/390 mainframe family. These machines are designed to run mission-critical enterprise applications.

The pSeries. This replaces the RS/6000 Unix server family. This series is designed for both traditional business apps and high-performance scientific computing. The pSeries can scale up considerably by upgrading to more powerful models and by clustering multiple pSeries systems together to achieve supercomputer performance. These systems can run AIX or Linux.

The iSeries. This replaces the AS/400 mid0range family. It continues to use the OS/400 operating system. The OS/400 is well-received since it includes many built-in apps that would otherwise have to be purchased separately. A major built-in app is the Universal DB2 database system.

The xSeries. This replaces the Netfinity family. These are the Intel-based servers that use from one to 16 processors.

eServer Clusters and Blades are not separate product lines but are considered extensions of these four series families. Clusters are configurations of multiple eServer systems connected together through high-speed links. Clusters have the advantage of combining the performance and capacity of multiple eServer systems while retaining the simplicity of managing them as if they were a single system.

eServer Blades utilize Intel microprocessors to make server blades that can be clustered together to deliver high performance in a modular and dense rack-mounted package.
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