Apple Updates iPad With Some Refinements SAN FRANCISCO - Apple updated the iPad on Wednesday with a high-definition screen, faster wireless connection and several other refinements. As recent history has shown, though, even relatively modest changes could be enough for the company to attract waves of new buyers for its tablet computer. The company said the new iPad would go on sale on March 16 for a starting price of $499, unchanged from the last generation of iPads. The product will have a screen that provides a comparable level of clarity to the iPhone's "retina display," with higher-resolution than conventional high-definition televisions, according to Apple executives. And in a sign that Apple intends to more seriously protect its market share in the tablet market, the company said it would continue to sell its second-generation iPad, dropping the price to $399 from $499. At a company event here, Apple also introduced a new version of Apple TV, the company's $99 set-top box for accessing Internet video, that streams movies in the sharpest of the high-definition video formats, called 1080p. The new tablet, called simply the new iPad with no numbers or letters following the name, is an effort to keep growth chugging along in a two-year-old business that has turned into a major technology franchise for the company. Apple's $9.15 billion in iPad sales over the holiday quarter were almost double the amount of revenue Microsoft brought in from its Windows software and not far from Google's total revenue as a company during the same period. Speaking from the same stage where Steven P. Jobs, the company's late chief executive introduced the second-generation iPad almost exactly a year ago, the company's new chief executive, Timothy D. Cook, said the iPad last quarter outsold the number of personal computers sold by any individual manufacturer. "In many ways, the iPad is reinventing portable computing and outstripping the wildest predictions," Mr. Cook said. The new iPad, the third generation of the device, looks virtually indistinguishable from its predecessor, without any of the bold outward design changes often associated with new Apple products. It features a faster processor - an A5X quad-core chip - and a higher resolution screen - 2,048 by 1,536 pixels, more than 3.1 million pixels, or four times more than the current iPad. It will also operate on the fourth-generation cellphone network technology known as LTE. In the United States, the new iPad will work on AT&T's and Verizon's networks. The iPad will also allow users to dictate e-mail, though Apple did not introduce an iPad version of Siri, an iPhone virtual-assistant feature that can schedule appoints and perform other tasks from natural-sounding voice commands. Last fall, Apple disappointed some pundits and enthusiasts by making mostly incremental enhancements with its latest smartphone, the iPhone 4S. That product ended up defying doubts to become a smash hit, leading to record sales over the holidays. During that time, Apple, based in Cupertino, Calif., solidified its lead as the most valuable company in the world, with a market capitalization of almost a half-trillion dollars, well ahead of its nearest rival, Exxon Mobil. The new iPad may show how durable Apple's hold on the tablet market is. For most of the two years the iPad has been on sale, Apple has faced a phalanx of competitors from Hewlett-Packard, Research In Motion, Samsung and Motorola, yet none has established a firm beachhead in the tablet business. A few of those competitors, like Hewlett, gave up. In a recent survey of American consumers with tablets by Forrester Research, 73 percent said they owned an iPad. That is a sharp contrast to the smartphone business, where Apple's market share has steadily eroded as phones based on Google's Android operating system have swept the market. Phones with Android software accounted for 51.6 percent of smartphone shipments worldwide in the fourth quarter, compared to 23.4 percent for the iPhone, according to Canalys, a research firm. Sarah Rotman Epps, an analyst at Forrester, said the iPad had maintained its grip on the market because most consumers bought it through retail stores rather than through wireless carriers. "Android smartphones are selling like hot cakes because that's what the carriers push," she said. With tablets, carriers are not the main destination for tablets. The new iPad, though, is likely to face more serious challenges to the product's dominance than in the past. Over the holidays, Amazon is estimated to have sold more than five million of its Kindle Fire, a smaller tablet that has attracted a new group of consumers to the category with a $199 price tag. Later this year, the first tablet devices to use Windows 8, a new operating system from Microsoft, are expected to hit the market. The software has been redesigned by Microsoft to take advantage of touch-screen devices. Apple sold 15.4 million iPads over the holiday quarter and has sold 55 million of the devices in total since they first went on sale in 2010. Mr. Cook told the audience Wednesday that Apple had sold 315 million iOS devices sold through end of 2011 and that iPads, iPhones and iPods are now responsible for 75 percent of the company's revenue. The chief criticism that some stalwarts of the PC industry have leveled at the iPad is that the device is not well suited for creating content, even if it is good for consuming it. Apple, though, sought to undermine that argument with a number of new apps. Those include a new version of its Mac software for editing digital photographs, iPhoto. A new version of Apple's GarageBand music software lets up to four people play together in a virtual band with iPads that are connected wirelessly.