Chapter 1
Advanced Application Architecture

The staying power of any computer system and its ability to protect the investment of its customers are the most important considerations in the purchase of a business computer. Businesses today find themselves caught up in a whirlwind of change. The introduction of new technologies, such as the Internet, has caused many businesses to change the very way they conduct their business. The only certainty seems to be continuous change. Technologies all around us will continue to change at an astonishing rate. Businesses need to protect themselves from the disruption that comes with change and at the same time find ways to incorporate those changes that can enhance their business.

Over the years, AS/400 customers have heard about the AS/400’s advanced architecture. They have also heard that it is the most adaptable architecture anywhere and that new technologies will continue to be incorporated into this system in a way that won’t have a negative impact on them or their business. While it is true customers have not had to change their application programs to take advantage of the new technologies, they often have not really understood — or cared about — how the system worked, as long as it worked.

Recently, the AS/400 architecture has once again come into the spotlight. The AS/400 is the first and only system in the world to have completed the transition to 64-bit computing. New models incorporate a type of processor architecture called a reduced instruction set computer (RISC). For comparison, the processors used in the original AS/400, along with other popular processors such as the Intel Pentium II and the Intel Pentium Pro, are known as complex instruction set computers (CISC).

RISC processors generally have simpler instructions than CISC processors, which means that very high-speed processors can be built at reasonable cost. The latest versions of RISC processors from all vendors are now 64-bit designs. The challenge is not designing and building the hardware. The challenge for the computer industry is how to enable existing software to take advantage of the new hardware designs. The AS/400 is the only system to have met this software challenge — all AS/400 applications are fully 64-bit enabled. No one else is even close.

When other computer vendors moved from CISC to RISC processors, they caused disruptions among their customers and independent software vendors (ISVs) who wrote application programs. Some application programs or parts of application programs had to be rewritten to move to the new hardware. This happened, for example, when Hewlett Packard (HP) introduced its Precision Architecture (PA) and when Digital Equipment Corporation (Digital) introduced its Alpha architecture.

To appreciate the magnitude of this disruption, consider Digital’s move to RISC. Digital estimated that moving its installed base to the Alpha architecture caused from 15 percent to 20 percent of the older VAX architecture applications to be rewritten. For any customer or ISV, application rewrites of this magnitude could be very costly.

In contrast, the AS/400’s technology-independent architecture protects the system’s customers and ISVs from such disruptions as they move to the new 64-bit RISC processors. Existing application software can immediately use the full capabilities of the new hardware. To see how this is possible requires a look at how the AS/400’s advanced application architecture differs from all others.

Computer Architecture

A Roman architect in the first century, Vitruvius, defined architecture as the act of designing a structure that had utility, strength, and the power to delight. The architecture of buildings and computers has this, and much more, in common.

Contemporary architecture owes much to the formal orders of classic architecture. Even the most futuristic designs spring from the past. The Egyptian pyramids, the Greek columns, the Roman arch, the Romanesque dome, and the Gothic pointed arch all furnish the foundation for creations we perceive today as the latest thing. In the history of computers, the ancient era starts only a few decades ago. As in building design, the most dynamic and exciting things happening today in computer architecture spring from discoveries and lessons learned from the “classics.”

The AS/400 architecture is based on a model developed more than a quarter of a century ago. Because of a flexible design approach at the outset, the AS/400 has been able to adapt quickly and dynamically to modern goals and needs. With its technology-independent architecture, the AS/400 has had, for years, features and capabilities other computer systems still haven’t achieved.