Perhaps at least partially as a result of those efforts, the mainframe remains a core system for high volume, high transaction processes, particularly those used in large financial services companies like Bank of America Corp.

[ Related: Now Departing: Union Pacific's 40-Year-Old Mainframe. ]

Kimberly Grim, senior vice president of mainframe engineering at Bank of America, describes mainframe systems, which handle the firm's most critical applications, as "very safe."

"We have been operating this platform for 40 years," Grim said. "It's changed a lot, and IBM has invested in keeping this platform state of the art." She said the mainframe platform can still handle high-volume work better than non-mainframe systems.

The Charlotte-based company said hundreds of its IT workers are assigned to mainframe tasks. It wouldn't be more specific on the number assigned to the platform.

IBM doesn't track the number of available mainframe related jobs, but it isn't hard to find advertisements seeking people with mainframe skills. For example, a search with the key word "mainframe" yesterday drew 97 help wanted ads on Monster.com. The jobs site said that 764 such jobs were advertised over the last 30 days. On Dice.com, a similar search produced 1,200 ads seeking mainframe experience over the past 30 days.

About four years ago, Grim said Bank of America saw a growing decline in the number of new college graduates with any mainframe training. That prompted the bank to become involved in IBM's Academic Initiative, which works with colleges and universities to develop mainframe training programs.

IBM said this week that 600 colleges, universities and high schools around the world are participating in the mainframe training program, which began in 2004.

The training initiative provides interns and new hires to Bank of America, while some members of its IT staff audit the initiative's courses and provide feedback to help tune the training to business needs.

IBM says it's mainframe revenue has grown in eight of the last 13 quarters. It did note that mainframe revenue plunged by 39% in the second quarter, mirroring server revenue declines for most vendors.

Competing vendors have been arguing that distributed systems have become a strong alternative to mainframes.

However, IT researcher IDC says that MIPS (Million Instructions per Second), a measure of processing power capacity used by mainframes, is on the rise. The mainframe is continuing to grow in terms of the amount of work that processed on the mainframe, which reflects improvements to the platform, said Tim Grieser, an analyst at IDC.