Microsoft, for its part, said that Apple gave the attack ads a short rest late last year after Microsoft unveiled its counterattack. Microsoft’s campaign, devised by the agency Crispin, Porter & Bogusky, initially featured the comedian Jerry Seinfeld and Microsoft’s co-founder, Bill Gates, and then a diverse collection of normal people proudly proclaiming, “I am a PC.”

Image A scene from Apples classic commercial that ran during the Super Bowl in 1984, its only showing. Credit... TBWA/CHIAT/DAY

“I think we confused them a little bit by embracing the stigma they put on our brand and then taking it in a different direction,” said David Webster, a general manager at Microsoft.

An Apple spokesman declined to comment about either company’s advertising.

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So far, Apple seems to be winning the fight. The Macintosh gained more than 2 percentage points of market share in the last year and now controls nearly 10 percent of the overall market for personal computers, according to the research firm Net Applications.

Apple’s ads have also fared better than Microsoft’s in the war for consumers’ hearts. In the last two months, Brand Keys, a market research company based in New York, queried 400 Apple and Microsoft users and measured their perceptions of Apple’s and Microsoft’s brand equity before and after seeing examples of the companies’ advertising.

Among the ads the firm showed were “Bean Counter,” an Apple spot that poked fun at Microsoft’s spending money on advertising instead of fixing product flaws. Brand Keys also surveyed responses to Microsoft’s first Seinfeld commercial, “Shoe Circus,” and the first “I am a PC” spot.

“Off the Air,” an ad that promised Apple stores would help customers switch from Windows to Apple’s Mac platform, was highly successful in lifting the brand equity that Apple users felt around the concept of “innovation, design and added value”  a factor that drives loyalty. The spot also improved PC users’ perception of Macs for their “trouble-free performance, service and support.”

On the other hand, Microsoft’s “Shoe Circus,” in which Mr. Seinfeld helped Mr. Gates buy shoes, failed miserably with consumers. After seeing the ad, both Apple and Microsoft users had a more negative perception of Microsoft in the areas of innovation, technology, trouble-free design, and warranty and pricing. “When you see an ad perform this poorly,” said Amy Shea, the executive vice president at Brand Keys who conducted the research, “you’ve got a real problem.”