The MacBook is a brand of Macintosh notebook computers built by Apple Inc. First introduced in May 2006, it replaced the iBook and 12-inch PowerBook series of notebooks as a part of the Apple–Intel transition. Positioned as the low end of the MacBook family, the MacBook is aimed at the consumer and education markets. It is the best-selling Macintosh in history, and according to the sales-research organization NPD Group in October 2008, the mid-range model of the MacBook was the single best-selling laptop of any brand in U.S. retail stores for the preceding five months.