SunGard Availability Services has tapped former AT&T executive Andrew Stern, 52, as its new boss. He replaces Eric Berg, who quit last winter, after three years, says corporate chief executive Cristobal Conde, who temporarily took over the unit, the largest provider of backup corporate computer systems.

Stern, an MIT-trained engineer (and Chicago MBA), most recently headed AT&T hosting and application services; he was previously chairman and chief executive of USintenrnetworking Inc., which AT&T bought four years ago.

Availability employs around 2,500, down 100 from this time last year, and about 12 percent of Wayne-based SunGard's total workforce. The business, which operates data centers around the U.S., faces competition from cheap online system protection arrangements. Other SunGard units offer financial, education and government services. The company is owned by a group of private-equity funds.