That's slowly changing. Like many companies, the bank conducts most software development projects on Windows or Unix servers. These distributed systems are more open, offer more-agile software architectures and are less costly to run and maintain than mainframes, Mulligan says. And distributed systems are increasingly offering traditional mainframe benefits, such as availability, scalability and server utilization. Mainframe technologies, ranging from channel architectures to virtualization, have migrated down to distributed systems and have begun to mature. "Most of the server solutions available today are morphing to become more like a mainframe," Mulligan says.

But the mainframe is also becoming more like distributed systems. Designs are evolving to incorporate technologies such as Fibre Channel, InfiniBand, Unix and Java. The success of those efforts will determine whether the mainframe will survive as a distinct platform or simply be absorbed into the world of distributed computing.

Robert DiAngelo, vice president and CIO at MIB Group Inc., says he doesn't trust distributed systems with his high-end applications for insurance fraud detection. "I'm in an environment that's easy to maintain, very secure, highly reliable," he says of his IBM z890 midrange system. DiAngelo is redeploying his applications in a three-tier architecture that includes Java, WebSphere and DB2. But the entire architecture, plus his development and quality-assurance testing environments, are consolidated into a single logical partition on the mainframe. Everything fits into a cabinet in his data center. "This is a lot easier to manage than 80, 90 or 200 servers that are spread out," says DiAngelo. MIB Group is a poster child for IBM's strategy of promoting the mainframe as a consolidation platform, although DiAngelo acknowledges that he's "out in front" of most organizations in taking this approach. As mainframe technologies trickle down to distributed systems, those systems are getting better at hosting mainframe-class applications. Meanwhile, IBM, Unisys Corp. and others are moving to more open, industry-standard technologies. Distributed systems based on Unix and Windows are eroding the low end of the mainframe installed base. The mainframe still firmly holds its edge in complex environments. But the battle for the midrange -- applications of up to 1,000 MIPS, where the majority of mainframe applications fal -- has already begun.

Unless the relatively high costs of mainframe hardware and software become more competitive, and unless more-agile software architectures, such as .Net and J2EE, can be successfully deployed on mainframe systems at scale, the mainframe could eventually be eased out of corporate IT. "IBM mainframes are going to become marginalized to the high end if IBM can't significantly reduce the cost," says Dale Vecchio, an analyst at Gartner Inc.

Adoption of industry-standard technologies is key to the mainframe's survival. IBM has based its strategy on Java, WebSphere and Unix/Linux and positioned the zSeries mainframe as a consolidation platform. IBM also released last July its System z9, which reflects an investment of more than US$1 billion and includes innovations such as an encryption processor and the ability to support up to 54 processors and 60 logical partitions. "That's an enormously impressive technology. They doubled everything except the price," says Gary Barnett, an analyst at Ovum Ltd. in London. While mainframes are incorporating additional open architectures, they're also likely to continue to be technology leaders, says Chander Khanna, vice president and general manager at Blue Bell, Pa.-based Unisys. "They are at the top of the waterfall. I don't foresee that changing," he says.