Surprisingly, Microsoft, which has never been known for running cool ads, has landed some punches. Shortly after the Microsoft campaign started, Apple unleashed commercials that mocked its competitor as spending money on advertising when it should have been fixing Vista, its much-maligned operating system.

“It got Apple’s attention, didn’t it?” says Robert X. Cringely, host of PBS’s NerdTV.

FOR years, Microsoft was the stodgy market leader. It sold 90 percent of the world’s operating system software, and generally left the advertising to Dell, H.P. and other hardware makers who licensed Windows. The only time Microsoft hawked its most recognizable brand on television was when the latest version of the software hit the shelves. Then the company flooded the airwaves with commercials full of loud music and swirling imagery saying that the new version of Windows is out  and that it’s awesome!

Apple is the classic smaller insurgent. Its share for desktops and laptops in the United States is just over 8 percent. Every time Apple grabs another point of market share from Microsoft’s partners, its stock price climbs. And one way that Apple has tried to gain share is by running clever ads that ridicule everything Microsoft stands for.

Image Credit... Photo illustration by The New York Times

There’s no better example than “Get a Mac,” unveiled three years ago by Apple’s longtime ad agency, TBWA/Chiat/Day. No technology company would choose Mr. Hodgman’s character, PC, to personify its brand. He reeks of the past. He boasts of using his desktop to make spreadsheets and ridicules his more youthful friend, Mac, played by the actor Justin Long, for using his desktop for “juvenile” pursuits like blogging and movie making  even through it’s clear that PC would like to be in on the fun. He just can’t get his Windows computer to do his bidding.

Like a classic sitcom character  think Ralph Kramden of “The Honeymooners”  PC is always dreaming up ill-advised schemes intended to show his superiority. He’s thwarted by viruses, system crashes and other problems more associated with Windows-based computers than Apple’s products  and, recently, he has become a hapless apologist for Vista. Mr. Long’s character smugly watches his friend’s pratfalls, glancing at the audience with raised eyebrows as if to say, “If only this poor guy would buy a Mac. . . .”

PC will never learn. Not as long as he keeps driving sales for Apple. Since 2006, the year that he first appeared in all his pasty-faced glory, Apple’s share of the computer desktop market in the United States has more than doubled, according to IDC, the technology industry research firm. Its stock price, meanwhile, has risen 142 percent since May 2006, while Microsoft’s has barely budged. Yes, the astonishing success of newer Apple products like the iPod and the iPhone has helped. But the PC character should also take a bow. (Representatives of Apple and TBWA/Chiat/Day declined to be interviewed for this article.)