But Dunham says it's not maintenance issues but changing software requirements that ultimately force most companies to upgrade equipment. Therefore, managing software upgrade cycles is key. As for computer hardware failures, "we haven't seen too many die," Dunham says.

At Bank of New York, Kahn says security software requirements have actually cut its computer life cycles from five to six years to four. "Right now, we're in a four-year life cycle on the vast majority of our equipment," he says, which is still longer than the average for most companies just a few years ago. Kahn says he'd prefer to keep the equipment even longer. "We have always historically kept [IT equipment] for a longer period of time," he says.

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