Apple's Macbooks had a strong back-to-school showing last quarter, as the company hit fifth place in IDC's global PC shipment charts.

Mac sales rose from 4.58 million in the third quarter of last year to 4.98 million this year, IDC estimated, allowing Apple to edge out Asus for the number five slot. (Rival research firm Gartner still has Asus in fifth place, with 5.77 million shipments last quarter. Hey, these are estimates.)

Overall, last quarter was fruitful for major vendors. Both IDC and Gartner estimated shipment gains for Lenovo, HP, Dell, Acer, and Asus, along with Apple. IDC attributed the gains to solid back-to-school sales, the continued Windows XP to Windows 7 migration for businesses, and a rise in low-cost PCs such as Chromebooks.

Why this matters: Unlike other PC makers, Apple's sales numbers aren't being buoyed by low-cost laptops. While IDC warns that the rise in cheap PCs are a "concern for the long term viability of vendors to adequately remain in the PC space," that concern doesn't apply to Apple, which tends to avoid racing to the bottom in pricing. For other vendors, the current situation contains echoes of the 2009 PC market, which grew fat on netbook sales and eventually crashed.

Win some, lose some

However, Apple has its own concerns as iPad sales are in decline. The company is rumored to be working on a larger version that might capture more of the PC market, but it may not arrive until next year, if at all. Apple is holding an event on October 16, where it's expected to announce minor upgrades to the existing iPad line.

Although PC shipments declined as a whole by 1.7 percent in the third quarter, this was entirely due to smaller vendors in the "other" category, several of whom have been scaling back lately. Since last year, Sony has sold its Vaio PC business to a smaller company focusing on the Japan market, Samsung has shut down its European PC business and Toshiba has said it will cut back on consumer PCs to focus on business users.