The MacBook Pro is a line of Macintosh portable computers introduced in January 2006 by Apple Inc., now in its third generation. Replacing the PowerBook G4, the MacBook Pro was the second model to be announced in the Apple–Intel transition, after the iMac. It is the high-end model of the MacBook family and is currently produced with 13- and 15-inch screens. A 17-inch version was available in the past.The first generation MacBook Pro appeared externally similar to the PowerBook G4, but used the Intel Core processors instead of PowerPC G4 chips. The 15-inch model was introduced first, in January 2006; the 17-inch model followed in April. Both received several updates and Core 2 Duo processors later that year.The computer's second generation, known as the "unibody" model, has a more tapered design and a casing made from a single block of aluminum. It debuted in October 2008 as the 15-inch MacBook Pro and the 13-inch aluminum unibody MacBook. The following January brought the design to the 17-inch model, along with the built-in battery that joined the rest of the MacBook Pro line in June, during which Apple also absorbed the unibody 13" Macbook into the MacBook Pro line. Subsequent updates brought upgraded Intel Core i5 and i7 processors and introduced Intel's Thunderbolt technology.