Apple has unveiled a new iPad with a high-definition screen. It said the resolution of the display was 2,048 by 1,536 pixels. The tablet is also powered by a new A5X chip with improved graphics performance. Chief executive Tim Cook claimed to have "redefined once again the category Apple created". Apple dominates the market but should face a fresh challenge later this year when tablets running the full Windows 8 system are expected to go on sale. The new iPad - which is simply called by that name - also features a 5-megapixel camera sensor. It will be able to run on 4G LTE networks where the service is available and can act as a wi-fi hotspot for other devices if carriers allow the function. It is 9.4mm deep, slightly thicker than the 8.8mm profile of the iPad 2. The basic 16GB model with only wi-fi will cost £399 and the top of the range 64GB model with wi-fi and 4G will cost £659. Apple's marketing chief Phil Schiller said the tablet has the same 10-hour estimated battery life as the previous model using only wi-fi. That limit shortens by an hour when using 4G. It is due to go on sale on 16 March in the UK, US, Canada, Germany, France, Switzerland, Hong Kong, Singapore, Australia and Japan. The previous model will stay on sale at a reduced price, starting at £329. Mr Schiller said that would make it more affordable for schools to buy the machine. The firm also announced an upgraded TV box which can now handle 1080p video. Films and TV shows will be sold via its iTunes store in the high-definition format. Mixed reactions IMS Research said Apple accounted for 62% of the global tablet market in 2011. Ahead of the press conference it said it expected that share to rise to 70% this year. Analysts at Gartner said they expected Apple to maintain its lead and increase the volume of tablets sold - but added that the launch did not contain any news to cause them to increase their "bullish" forecasts. "I'd call the new iPad an evolutionary device with some revolutionary experiences," said research director Michael Gartenberg. Others expressed disappointment following the news noting that the new device's display did not include haptic touch-feedback technology or access to the iPhone 4S' voice-controlled Siri "intelligent assistant" as rumoured. "As tablets are increasingly being used for personal media consumption, it is promising to see a better screen resolution," said Fred Huet, managing director of Greenwich Consulting. "But will this be enough to ensure Apple's competitive lead in the marketplace? No." However, the new iPad won praise from journalists at Engadget who were among the first to try out the tablet. They noted that the improved screen resolution should lead to improved apps. "Apple just put an insane amount of real estate in the hands of crafty developers, and frankly, we can't wait to see what they cook up," wrote Darren Murphy. Apple's shares closed 0.08% higher on Wall Street at $530.69.