NEW YORK » Apple Inc. shook up its executive ranks today, saying the head of its store operations is leaving after just six months on the job. In addition, the long-serving head of its iPhone software development operations is exiting next year.

Retail head John Browett was the CEO of British electronics chain Dixons before joining Apple. The Cupertino, Calif., company didn’t provide a reason for his departure. The stores will report to CEO Tim Cook while the company looks for a replacement, Apple says.

Scott Forstall was senior vice president of iOS software and joined Apple in 1997 with its purchase of Steve Jobs’ NeXT startup. The company credits him as one of the original architects of Mac OS X. Craig Federighi, who is now in charge of the Mac OS, will add iOS development to his responsibilities, Apple said.

Forstall will act as an advisor to Tim Cook until he leaves, Apple said. The company didn’t provide a reason for his departure either.

Parts of Forstall’s responsibilities will be spread among other top Apple executives. Jony Ive, the chief designer behind the distinctive look ofApple hardware, will take responsibility for the look and feel of Apple’s software as well.

Eddy Cue, head of Apple’s online services, will assume responsibility for Siri, the “virtual assistant” application on the iPhone and iPad, and Maps, Apple’s navigation application. Maps launched in September and quickly drew unfavorable comparisons to the software it was replacing, Google Map.

Browett took over the store operations after Ron Johnson, who helped create the Apple stores, left to become CEO at J.C. Penney Co. in November.

Apple has more than 360 stores, and they’re unique in several ways. They sell more per square foot than any other chain in the U.S., yet they account for just 12 percent of Apple’s overall sales. They’re ambassadors of Apple’s brand, and provide customers with an easy way to access in-person technical support. At the time Browett was appointed, commentators wondered what an executive from a traditional retail operation would bring to Apple.