Apple has likely been softening the computer market share growth of its top rivals during the summer, according to early IDC estimates. The company's portion of the market is estimated to have shot up from 7.3 percent in summer 2007 to 9.1 percent just a year later, giving it the single largest growth by an individual computer builder of the top five with just over 1.65 million Macs shipped and a 32 percent total boost. By comparison, top-ranked Dell has moved just a tenth of a percent upwards to 29.2 percent (5.3 million PCs) while second place HP actually declined by a similar amount to 25.1 percent (4.55 million) in the summer.

Fourth-place Acer's share grew the most of the five, jumping from 4.2 percent to 8.5 percent (1.54 million PCs), but was accomplished primarily though its buyout of Gateway. When both companies are factored into the results, the unified Acer is predicted to have lost its third-place standing and dropped from 9.2 percent.

Toshiba, which regularly occupies fifth place, also lost a small amount of share year-over-year and declined a tenth of a percentage point to 5.4 percent of US shipments or 978,000 systems.

As is common in its reports, IDC doesn't explain the differences in results but does mention that modest help came from back-to-school sales. It also notes that Dell's overall performance was hurt by its still heavy emphasis on direct sales in a poor economy.

Apple continues to sit outside of the top five in the world, however, and would need to outpace Toshiba's estimated 4.6 percent of world market share, or 3.66 million shipped PCs. HP leads the field 18.8 percent and nearly 15.1 million PCs while Dell, Acer, and Lenovo fill out the middle of PC rankings.