Dell Inc. Chairman Michael Dell vowed yesterday to "do better" after the world's biggest personal computer maker posted second-quarter earnings that fell by half amid a bruising price war with rival Hewlett-Packard Co.

The company also disclosed an informal Securities and Exchange Commission investigation into its accounting — deepening worries that the tech-industry juggernaut may be stalling.

As the company slashed prices to spur sales, some customers have complained that Dell also cut back on customer service. And while HP benefited from a recent rebound in retail sales, Dell's direct-sales model — traditionally one of its competitive advantages — hindered its ability to connect with buyers of low-end machines.

"We are clearly disappointed with our financial results," said Kevin Rollins, Dell chief executive. "We were overly aggressive in a slowing marketplace, and in a situation where component prices didn't come down as we thought."

Dell shares slipped more than 5 percent to $21.60 in after-hours trading yesterday following the earning announcement. They rose 7 cents to $22.80 during regular trading. They have fallen nearly 24 percent this year.

Dell reported a profit of $502 million, or 22 cents a share, compared with $1 billion, or 41 cents, during the same period last year. Sales rose 5 percent. The result matched analysts' expectations, which they had greatly lowered last month after Dell warned that price cuts would hurt margins.

That announcement sent Dell shares down 10 percent, their biggest decline in six years.

But even as they punished Dell, investors have rewarded HP, which has had its product lines reorganized and staff trimmed under chief executive Mark Hurd. HP posted strong profit growth and its shares rose 72 cents, or 2 percent, to $35.15 yesterday. HP shares have climbed nearly 23 percent this year.

Dell also took a hit this week when it recalled 4.1 million laptop batteries that the company said could catch fire, after at least six in the U.S. apparently did.

"To recall the batteries was the right thing to do," Rollins said. "We recalled a much larger quantity than the specific incidents would require."

Dell also said it had increased, to $150 million from $100 million, the amount it planned to spend on customer service improvements. The company does not issue financial guidance.

"We're not satisfied with our performance, and we will do better," said Dell, the company's namesake founder who relinquished the title of chief executive to Rollins in 2004.

Dell started selling computers out of his University of Texas dorm room when he was 19, and dropped out of school to concentrate on the business in 1984. Rollins joined the company in 1996. For much of the past decade, the duo presided over sharp growth that made the company a bright spot even as the rest of the tech industry stumbled after the dot-com boom.

The company also disclosed yesterday that the SEC, in August 2005, had sent notice of a informal investigation into Dell. In the process of responding to requests for "information relating to revenue recognition and other accounting and financial reporting matters for certain past fiscal years," Rollins said, the company recently found information that raised "potential issues."

Dell said it doesn't believe the issues will materially impact its financial results, but nevertheless its audit committee launched an independent investigation.