Acer ahead of its formal keynote has unveiled two ultrabook-class systems. The Aspire S5 is billed as the world's thinnest ultrabook and measures just under 0.6 inches thick. The black, magnesium-and-metal body weighs 2.97 pounds. Along with the thinnest, Acer touts the S5 as one of the first Windows-based ultrabooks to carry Thunderbolt, which it backs with USB 3.0.
