Mainframes might not be enormously fashionable in an era of cloud computing but they still loom large in the enterprise computing world, as they tend to be home to essential applications and data.
But as the generations with mainframe skills age, finding ways to replace them has been increasingly tricky.
That goes for IT vendors as well as end user organisations – for example it's been an issue for CA Technologies as mainframe management is still a big part of its business (accounting for half of its revenue and three-quarters of its profit).
Adam Elster, CA's executive VP of mainframe told TechRepublic that for many companies that had them, the mainframe still makes sense.
"We are seeing that the big mainframe sites that are the backbones for these organisations those are getting bigger. There's no really compelling event for them to migrate off the platform – there's no return on investment," he said, speaking at the company's CA World customer event in Las Vegas.
He said that because mainframes can sit - for example - at the back of banking systems, adding internet and mobile banking can mean mainframe transaction volumes are going up, not down.
But Elster said one of the big challenges is finding software engineers with the right skills. He said CA spent several years trying to search for a 25 year-old who had five years experience of the main frame - and didn't find very many of them.
"It's like looking for a unicorn," he said.
"So we started a very aggressive associate mainframe software developer programme with college graduates and we train them and we mentor them and right now my largest mainframe development centre is in Prague and the average age is under 30."
In contrast, the average age of engineers at one of its US sites is closer to 50.
"We hire six, 12 at a time and after several years we think that's going to help us build out the next generation and protect our future as well," he said.
TechRepublic attended CA World as a guest of CA Technologies.
Steve Ranger is the UK editor of TechRepublic, and has been writing about the impact of technology on people, business and culture for more than a decade. Before joining TechRepublic he was the editor of silicon.com.