This was the first case of keyboard internal backlighting seen on a notebook computer. Year 6 is the entry year for the notebook computer program. It is optimized for power efficiency, a vital characteristic for extending notebook computer battery life. The Switchblade opens up and closes like a notebook computer. During this time it was allegedly the best audio system available in a notebook computer. The first notebook computer containing GlidePoint appeared soon thereafter. The MacBook Air is Apple's least expensive notebook computer. The Lenovo IdeaPad U310 is an Ultrabook-class notebook computer released in 2012. Seiko's notebook computer, known as the HC-20 in Japan, was announced in 1981. Similarly, the less-common term "whitebook" denotes a notebook computer assembled from off-the-shelf parts.