The MacBook Air is a line of Macintosh ultraportable notebook computers from Apple Inc. The Air was designed to balance both performance and portability, consisting of a full-sized keyboard design, a machined casing made of aluminium, and a very light and thin structure. The MacBook Air is available in two sizes, with the length of the diagonal display determining the model size: 13.3-inch and 11.6-inch (or 33.78 cm and 29.46 cm, respectively). A range of model choices with different specifications are produced by Apple, and as of 2014, all Air models use solid-state drive (SSD) storage and Intel Core i5 or i7 central processing units (CPUs).In the Macintosh product line, the MacBook Air sits below the thicker and higher-performance MacBook Pro. The MacBook Air was originally released as a premium ultraportable which was positioned above the white MacBook. Since then the MacBook Air has become Apple's entry-level laptop due to the discontinuation of the white MacBook in 2011, as well as lowered prices on subsequent iterations of the MacBook Air. In recent years the MacBook Air has become the best-selling Macintosh computer and the best-selling ultraportable being credited with revolutionizing lightweight yet powerful laptops known as Ultrabooks.