Chief Executive Tim Cook, presiding over his second major product launch since 2011's voice-enabled iPhone 4S, introduced the highly anticipated third iteration of the tablet, which is available for pre-orders from Wednesday and will hit store shelves March 16.

The high-end model of Apple's latest iPad will be capable of operating on a high-speed 4G "LTE," or Long-Term Evolution, network. At speeds roughly 10 times faster than current 3G technology, that may help banish the sometimes shaky video quality of older devices.

Wall Street had anticipated many of the features Cook showed off on Wednesday, including a higher-definition "retina display" screen and a better camera.

Shares in Apple traded 0.5 percent lower at $527.50. They hovered around $530 throughout the proceedings, which were attended by Marc Benioff, CEO of enterprise cloud computing company Salesforce.com Inc; Jeremy Stoppelman, CEO of online business review site Yelp Inc; and influential venture-capitalist John Doerr, among other industry luminaries.

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Some had held out hope of a positive Apple surprise, recalling late CEO Steve Jobs and his now-iconic "one more thing" unveils at the very end of the proceedings. Others said the upgrades and tweaks to the iPad could only go so far in fending off hard-charging competition.

"While the hardware is notably enhanced, with an impressive retina display, better camera and faster processor, there are still some areas of improvement that Apple needs to work on, in order to stay ahead of its encroaching competitors," said Greenwich Consulting managing director Fred Huet.

"As tablets are increasingly being used for personal media consumption, it is promising to see a better screen resolution. But will this be enough to ensure Apple's competitive lead in the marketplace? No."

Others say Apple is betting a 4G-equipped iPad will tempt more U.S. consumers to pay for higher-quality video on the go. That, in turn, should give the Verizon Wireless venture of Verizon Communications Inc and Vodafone Group Plc and AT&T Inc a revenue boost, analysts say. Verizon Wireless and AT&T will host and sell 4G wireless plans to 4G users.

Until now, buyers have been reluctant to shell out extra cash even for iPads with slower 3G connections. The cheaper WiFi-only model -- with much more limited Web access -- is by far Apple's top-selling one today.

An updated version of the WiFi -only model remains at $499. The most expensive 4G model, with 64 gigabytes of storage, will go for $829. The previous iPad2 with 3G also sold for $629 to $829, apart from the WiFi only model. The cheapest model of the previous-generation iPad 2 now retails at $399.

"The iPhone 4S showed us that Apple doesn't need to out-do itself with new product designs to continue extending its domination of a category," said CCS Insight analyst John Jackson.

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The company is counting on a warm reception to its latest tablet to fend off an increasingly aggressive challenge from tablets powered by Google Inc's Android technology, with Microsoft Corp software-driven devices slated to come soon.

"Everyone's been wondering who will come out with a product that's more amazing than the iPad 2," Cook said.

"Stop wondering: We are."

Earlier in the session, Cook again held forth on what he called a "post-PC world," in which users move increasingly away from traditional desktop and laptop computing and toward an array of portable devices, including tablets.

Smartphones and tablets are starting to eat into PC sales as mobile technology gets more advanced and available content expands.

Some experts believe mobile devices, as they get more powerful, will eventually displace PCs in many markets, hurting business for the likes of Hewlett-Packard Co and Dell Inc.

The global tablet user base reached 67 million in 2011, according to researcher Strategy Analytics. Analysts expect double-digit growth in tablet sales in coming years.

Cook also announced that the company's new $99 Apple TV set-top box, a concept that late CEO Steve Jobs had called a "hobby," now supports high-definition 1080p screen technology.

"Last year alone we sold 172 million post-PC devices," Cook told the audience at the Yerba Buena Center in downtown San Francisco, Apple's preferred venue for product unveilings.

"And this made up 76 percent of our revenues. This is incredible."

(Additional reporting Noel Randewich in San Francisco, Nicola Leske and Sinead Carew in New York, and Bill Rigby in Seattle, Writing by Edwin Chan; Editing by Gerald E. McCormick)

SOURCE: Poornima Gupta and Alexei Oreskovic, REUTERS