They process credit cards, send orders to computer screens in kitchens and help run loyalty programs. In the industry, they're called point-of-sale, or POS, systems, and vary greatly in what they can do.
The register malfunction that forced Starbucks to close stores last week was surprisingly large; it affected all company-owned stores in the U.S. and Canada, or more than 60 percent of roughly 13,500 locations.