Who'll mind the mainframes?

They're the grizzled, unglamorous veterans of the computing world, middle-aged men and women who don't create best-selling computer games or dazzling special effects for the movies. All they do is quietly run the most important computer systems in the world.

They operate mainframe computers, the ''big iron" machines that run businesses and governments all over the planet. Mainframes issue Social Security checks, track credit-card purchases, and oversee the nation's air-traffic network. They're immensely powerful computers, and immensely reliable, routinely running around the clock for years at a time.

But many mainframe operators have been at it for decades, and they've begun to realize that their time is running out.

''Some of us started dying," said Robert Stanley, 56, director of research for Air Traffic Software Architectures Inc. in Ottawa. ''Heart attacks and the like. Thirty years of Twinkie-eating."

Stanley sits on the board of directors of SHARE Inc., an organization of mainframe computer users which is meeting in Boston this week. Founded in 1955, SHARE is probably the oldest computer users' organization on earth -- in more ways than one. Indeed, Stanley said that 80 percent of the 1,300 conference attendees are 40 or older.

Amid concerns that America doesn't produce enough technically trained young people, mainframe computer users and developers are especially concerned. Most computer science students concentrate on small-computer technology, such as Microsoft Corp.'s Windows operating systems, or the popular alternatives Unix and Linux. Few have been trained on zOS, the operating system that runs IBM Corp.'s massive mainframes.

One of the few young people at the conference, 26-year-old Lamonia Whitaker of Columbus, Ga., never had to learn about mainframes while earning her computer science degree at Columbus State University. ''I don't even think they offer mainframe courses anymore," said Whitaker, a database administrator at Total System Services Inc., a credit-card processing firm.

Stanley and other mainframe partisans say that media hype is partly to blame. During the Internet boom of the late 1990s, many industry pundits declared that mainframes were obsolete, destined to be replaced by clusters of smaller, cheaper machines using personal computer technology. Indeed, smaller computers supported many of the hot Internet companies like eBay and Amazon.com. Students clamored for training in Windows and Unix technologies, and colleges redesigned their course offerings.

But the pundits were wrong. Traditional mainframe users have remained loyal to the technology. That's good news for the venerable computer giant IBM Corp., by far the leading maker of mainframe machines. After getting clobbered in desktop computers by nimble businesses, IBM recently sold its money-losing desktop computer business to the Chinese company Lenovo Group Ltd. But IBM still makes lots of money from its mainframes. According to the research firm Gartner Inc., IBM sold $4.5 billion worth of them in 2003 and $5.3 billion last year.

Mainframe sales have slumped in the first two quarters of 2005, but it's probably because customers were waiting for IBM to unveil its latest upgrade. The new machine, called Series z9, is on display at the conference, and goes on sale next month.

Big companies still love mainframes. Unlike desktop PCs, these machines are designed to deliver near-perfect reliability. They can be repaired or upgraded while still running, and their software is vastly more stable and reliable than that found on desktop machines. In addition, mainframes use massive data channels that let them process immense amounts of information. This makes them perfect for banks, airlines, or any organization that must track millions of transactions.

Another strength of mainframes is ''virtualization," the ability of one large machine to act like hundreds of small computers. ''You can run multiple workloads and multiple applications together on the same box, sharing resources," said IBM mainframe marketing director Mike Bliss. For instance, mainframes can run the popular Linux operating system as well as any desktop machine.

Colin Rankine, mainframe analyst at Forrester Research in Cambridge, said that the actual number of companies and organizations that use mainframes has declined. ''But the user organizations are increasingly large," Rankine said. ''The largest organizations are the ones that are most loyal to the platform."

But to run the latest mainframes, IBM and its customers need a few thousand youngsters to replenish the ranks.

''There's a lot of gray hairs running around here," said mainframe programmer Frederick Dombrowski as he looked around the SHARE conference at Hynes Convention Center. (The acronym SHARE does not stand for anything; according to organizers, it refers to sharing information.)

Dombrowski, who works for Bank of America Corp. in Richmond, Va., has been programming mainframes since 1977, and wonders who will fill his shoes. ''If mainframes are going to be in the future, then younger people are going to have to learn it," he said.

But with few colleges offering mainframe courses, most young people aren't prepared for the complexity of mainframes. ''Very rarely do you see a new hire that's directly out of college," he said.

Companies are taking matters into their own hands. Whitaker learned her trade at age 18, through an intensive six-month training course sponsored by Total System Services, her future employer. The experience made her a devotee of the big machines.

''I'm not a computer nerd, but I do love what I do on the mainframe," Whitaker said. ''PCs do not interest me."

Hiawatha Bray can be reached at bray@globe.com.