Chief Executive Steve Ballmer said Microsoft Corp. needs to do better in the market for tablet computers that Apple Inc. has found success in with the iPad.

"We've got to make things happen" with Windows on such devices, Mr. Ballmer said at a conference for investors on the company's Redmond, Wash., campus. "We're in the process of doing that right now."

Mr. Ballmer said Microsoft is working closely with hardware partners to improve the quality of tablet devices that run Microsoft's Windows 7 operating system. The software giant, which currently has four retail stores, is also planning to open three more, he said

Tablet or slate devices—thin, keyboard-free computers with touchscreens—running Windows 7 haven't caught on yet, as computer makers struggle to create products with the responsiveness and ease of use of the iPad.

Apple has done an "interesting job" with the iPad, Mr. Ballmer said, adding "they've certainly sold more than I'd like them to sell."