IN 1991, Stewart Alsop, the editor of InfoWorld and a thoughtful observer of industry trends, predicted that the last mainframe computer would be unplugged by 1996. Last month, I.B.M. introduced the latest version of its mainframe, the aged yet remarkably resilient warhorse of computing.

Today, mainframe sales are a tiny fraction of the personal computer market. But with the mainframe facing extinction, I.B.M. retooled the technology, cut prices and revamped its strategy. A result is that mainframe technology — hardware, software and services — remains a large and lucrative business for I.B.M., and mainframes are still the back-office engines behind the world’s financial markets and much of global commerce.

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