IBM is already monetizing its Watson super computer in health care and a number of other industries, but the road to profitability will improve over time, IBM CEO Ginni Rometty said on Friday.

"It's a service, so it ramps up over time by it's nature," she told CNBC's Becky Quick. "This will be a play for the long run."

Rometty made her comments from Berkshire Hathaway's annual shareholder meeting in Omaha, Nebraska, where Watson, IBM's predictive data analytics service, was on display.

Berkshire Chairman and CEO Warren Buffett revealed to CNBC in 2011 that he had purchased about 64 million shares of IBM stock for about $10.7 billion. This past weekend, he said he had continued to build that position in the first quarter, purchasing about 3 million additional shares to bring Berkshire's total stake in IBM to roughly 78 or 79 million shares. The company has not yet publicly disclosed the exact figure for its latest purchases in Securities and Exchange Commission filings.

"I bought it because I thought we were getting our money's worth," he said.

Read more Buffett-related stories

Live Blog: Buffett on repurchases and dividends

Buffett: THIS is keyto valuing stocks right now

Buffett helps us see the future: 4 blue chip CEOs

Buffett hits back at Clayton Homes lending gripes