An Ultrabook is a high-end netbook built to a specification defined by Intel. All Ultrabooks have Intel Ivy Bridge processors, featuring low power consumption and integrated graphics. They have a unibody chassis which is less than 0.8 inches thick. Screen size is generally 11 or 13 inches, although 15 inch models are expected to be produced in future. Battery life is 7 hours or more.
Ultrabooks use solid-state hard disks (SSDs) which are much faster than traditional magnetic disks.The standard Ultrabook operating system is Windows 7. The Ultrabook design and specification is very similar to Apple’s MacBook Air laptops.
Intel has established a $300 million fund to be spent over the next three or four years in areas related to Ultrabooks. This is aimed at reviving a flagging netbook market and fighting off competition from the Apple iPad and Android-based tablets which normally use ARM processors.
One of the first Ultrabooks to appear on the market was the was the Asus Zenbook UX21 which weighs 2.1 pounds and has a 128 GB SSD, an 11.6-inch display and an Intel Core i5 processor. A higher-end model, the UX31, has an Intel Core i7 processor and has a 256GB SSD and a 13-inch display with a resolution of 1600 x 900 pixels.
Another early arrival was the Acer Aspire S3 which has an Intel Core i5 processor, 4GB of memory, and a hybrid hard drive (20GB SSD and 320GB SATA HDD). It weighs about 3 pounds and is just over half an inch thick.
For further information see the Wikipedia article on Ultrabooks.