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ROCHESTER, Minn. - Today, it would be easy to dismiss the long-retired System 38 computer as ancient iron. But many engineers who know what's under the skin of the latest iSeries servers instead credit a System 38 innovation with nothing less than keeping the Rochester-produced machines up with current technology - a quarter century later.

The 25th anniversary of the long-retired business machine passed without official fanfare at its cradle on the city's northwest side. Its "virtualization architecture" admittedly could seem esoteric for the masses, even at a computer complex.

Yet that breakthrough has enabled the current IBM iSeries line and its predecessor generation, the AS/400, to cope with the radical changes ranging from operating systems to underlying processors, said iSeries marketing manager Ian Jarman.

The architecture is a specially coded layer sandwiched between the software programs used by the computer and hardware itself - processors, memory, etc.

The engineers and programmers in 1978 essentially built a type of "buffer zone" for change, he said.

"They understood that any individual hardware technology would become obsolete, so they needed to find a way to have a system that could adapt to disruptive (new) technologies without disrupting the applications and business of our customers," Jarman said.

The design enables the task software to work without knowing anything about the hardware underneath. For example, an operator can save a document without knowing its exact location in a disk drive or the computer's memory banks. The computer takes care of that automatically.

The same architecture more recently was key to IBM's move to equip the iSeries for different operating software such as Java and, recently, Linux. Next year, IBM's version of Unix, called AIX, will be added, the company has announced.

The design also plays a role in the computer-maker's newest thrust - capacity on demand.

It allows users to turn processors on and off to cope with temporary surges in data. The trick is to automatically bring reserve processors on line without interrupting the computer's work, Jarman said.

The architecture likely will have a much longer useful lifespan. The current iSeries has been equipped with 64-bit technology since 1995. The virtualization layer is designed for maximum data flows of 128 bits, though it is implemented in 64 bits to match the current machines.

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