There are about 2,000 attendees at the conference, which is sponsored by research firm Gartner Inc., and many of them are from large companies that continue to rely heavily on heterogeneous IT environments -- despite a push by many vendors toward industry-standard servers. In fact, when asked whether they run their environments on either Windows or Unix exclusively, only 4 percent said yes.

Abdul Khan, who manages servers and storage for Blue Shield of California, said the San Francisco-based insurer relies on mainframe systems. "It's an integral part of our legacy systems," said Khan, whose mainframe environment supports custom-written applications that would be too difficult to move to other systems. "It would take a long time to change our software."

Khan also said he believes that mainframe systems continue to lead in terms of reliability.

Another mainframe advocate is Bill Homa, CIO at Hannaford Brothers Co., a US$5 billion grocery retailer and one of the first companies to implement IBM's new zSeries z9 mainframe.

Homa's z9 was installed four weeks ago and is an upgrade from an earlier mainframe. It is one of two IBM mainframes at the Scarborough, Maine-based company, part of an IT environment that includes 200 Unix AIX servers and about 250 Windows servers.