Updated MacBook Airs should be a major driver of Mac sales in the second half of the year, says Barclays analyst Ben Reitzes. "For the September quarter, we estimate Mac unit sales to grow 18% y/y [year-over-year], which may be conservative given anticipation for the MacBook Air," he writes in a new memo. The Air has proven especially popular since its 2010 overhaul, which included an 11-inch option starting at $999, equivalent in price to the now-defunct white plastic MacBook.