Apple thinner iPad Air and retina iPad Mini

Apple has unveiled a top-of-the-range tablet called the iPad Air that is 20% thinner than the previous version.

The 9.7in (24.6cm) computer is 7.5mm (0.3in) thick and weighs 1lb (469g), which the firm claims is the lightest full-sized tablet on the market.

It is powered by the same A7 chip found in the company's iPhone 5S.

The launch comes at a time when some analysts have suggested that Google's Android is about to overtake Apple's iOS as the bestselling tablet platform.

Apple also announced a new version of its iPad Mini.

Its 7.9in (20cm) screen has been upgraded to feature 2048 by 1536 pixels - the same as the larger model. It is being branded as "retina" to highlight the increased resolution.

Amazon and Google have already announced small tablets - the Kindle Fire HDX and Nexus 7 - with similar high definition displays.

"We've got the retina upgrade to the smaller iPad that many thought should have been there in the first place," Tony Cripps, principal analyst at tech consultants Ovum, reflected after the announcement in San Francisco.

iPad Mini

The iPad Mini's new screen has 326 pixels per inch, similar to the 323ppi resolution of the Nexus 7

"Market share slip is inevitable because so many rival devices are coming out, which is not necessarily a bad thing as the overall sector is growing.

"Apple does now have a cheaper model thanks to it offering the original iPad Mini at a lower price - but the firm doesn't really want to go to the low-end because that's not where the greatest profit is extracted."

Apple also announced that the latest version of its Mac operating system, Mavericks, would be offered at no cost to owners of computers already running any version of OS X released since 2009. It is the first time the company has not charged for a major Mac OS upgrade.

By contrast the full version of Windows 8.1 is sold for about £100, although it is free to existing Windows 8 users.

Linux-based Ubuntu has always been offered without charge. Chromebook computers also get free upgrades for Google's PC operating system.

New laptops, productivity and leisure apps were also unveiled. However, Apple did not show off a new TV set-top box as some had speculated.

Tablet competition

The California-based firm's most recent financial release said that its iPad range accounted for $25.8bn (£17.6bn) worth of sales in the nine months leading up to July.

That represented 19% of its revenue for the period.

However, Apple acknowledged that the amount of money it was making from the product line was growing three times slower than the growth in unit sales since many customers were opting for its cheaper iPad Mini and iPad 2 models rather than its top-of-the -range "retina display" versions.

Tim Cook

Apple chief executive Tim Cook said the firm had sold more than 170 million iPads

It also faces the fact it is losing market share to rivals.

Apple's iOS operating system accounted for 53.9% of all tablets shipped in 2012, according to Gartner.

The tech research firm forecasts that Android will become the market leader with a 49.6% share, versus Apple's 48.6% this year, adding that it expects that gap to widen further in 2014.

However, consultants at IHS iSuppli said those figures needed to be put in context thanks to Apple's success at making money by taking a cut of app sales.

"It is in terms of revenue per active device where Apple's lead is strongest," said the firm's mobile media analyst Jack Kent.

"An iOS device generates around three to four times as much app revenue through Apple's App Store as an Android device through Google Play.

"Apple has so far offered a more compelling range of tablet-specific content, but Google is clearly looking to address this."

He added that many Android tablets, including Amazon's Kindle and most products sold in China, did not have Google's store pre-installed.

Apple's chief executive Tim Cook noted there were now 475,000 apps designed for iPads available through its online marketplace.

Craig Federighi

Apple's software chief Craig Federighi said the new Mac OS X Mavericks system would extend laptops' battery life

But another market watcher suggested that Apple's priority remained securing a "premium" margin on the shop price of its hardware, and that add-on software sales were of secondary interest.

"Some players, like Amazon, can afford to slash prices because they have a different business model based on content and commerce," said Thomas Husson, from the tech industry analysts Forrester.

"While Apple has shared $13bn to developers since 2008, it has made less than $6bn out of apps.

"It's a huge stat, but low in comparison with Apple's quarterly results."