ASUS recently rolled out its latest notebook series called the Zenbooks. These ultrabooks are already available starting today with a $999 starting price. The UX21 is a potential MacBook Air 11.6-inch because of the size while the UX31 is going against the 13.3-inch Air.
Features of these lightweights notebooks include aluminum alloy bodies, all-metal keyboards, glass trackpads, ultra low voltage Core i5 and i7 processors, stereo speakers with ICEpower technology by Bang and Olufsen, SATA III SSD, Bluetooth 4.0, USB 3.0 connectivity, 4GB RAM, 1366 x 768 and 1600 x 900 resolutions, and 5- and 7-hour battery life.
You can actually choose from three configurations of the UX31 while the UX21 has a couple. The difference lies on the processors and the solid state storage capacities.