Instead, the MacBook Air uses what’s called flash storage, a more efficient but pricier technology used in many of the company’s other portable products. That costliness is evident in the base model, which only has 64 gigabytes of space. (It costs an extra $200 to double the storage.)
This flash memory helps the new MacBook Air achieve between five and seven hours of battery life when surfing the Web, and 30 days of standby time. That also allows the computer to turn on almost instantly.
See full story here: http://edition.cnn.com/2010/TECH/web/10/20/apple.mac.event/index.html