"Expansion and changes
Originally, Apple Stores contained a dedicated point-of-sale (POS) station. However, in 2006, Apple began introducing a new store layout and design with surgical-grade stainless steel walls and backlit signage. The new store design replaced the dedicated point-of-sale station with the handheld EasyPay system. A dedicated point-of-sale station still exists in most of these stores to facilitate transactions not paid for by credit card.[23][24] The Regent Street store has more point-of-sale terminals than any other store. Only flagship stores and a few older locations have a dedicated point of sale; all other stores have a POS behind the Genius Bar. Apple has recently changed their EasyPay systems to operate on iPod Touch instead of the previous Windows-based system. The iPods feature a custom housing, the Infinite Peripherals Linēa-Pro barcode scanner and card reader, to allow the same transactions on the iPod."
From http://en.wikipedia.org/wiki/Apple_Store