Microsoft has unveiled Surface - its own-brand family of tablets.

The touchscreen computers will be powered by its upcoming Windows 8 system and contain a choice of an Intel or ARM-based processor.

It allows the firm to challenge Apple's bestselling iPad with a device that can run standard applications such as its own Office programs and Photoshop.

But it puts Microsoft in competition with other manufacturers planning to release tablets designed for Windows 8.

The company's chief executive, Steve Ballmer, said he had wanted to give the software "its own companion hardware".

The devices have 10.6 inch (26.9cm) displays, built-in kickstands and are housed in magnesium cases - which the company described as the first of their kind.

The ARM-based tablets are 9.3mm (0.4 inches) thick - slightly less than the iPad - and run the Windows RT version of the new system. The Verge reported that the chipset will be built by Nvidia. Third-party developers must rewrite programs from scratch to run on the system's Metro interface to work on these devices.

The versions using Intel's x86 technology run Windows 8 Pro and are 13.5mm (0.5 inches) thick. These can run Metro and an updated version of the "classic" desktop meaning they can use software designed for earlier editions of Windows, although some programs will need to be updated to be compatible.

The specifications mean the Surface tablets have bigger screens than the iPad but are heavier.

Pen input

A variety of accompanying covers can be attached using built-in magnets. They double as keyboards with trackpads. One version is flat while the other offers keys that can be depressed.

The devices are also designed to work with a pen accessory using what the firm dubbed "digital ink". When the stylus is held close to the screen of the tablet it ignores touch-input from the users' hands and "samples" the ink at 600dpi (dots per inch).

The ARM-based version will be available with either 32GB (gigabytes) or 64GB of storage. Microsoft said they would be priced at a similar rate to other tablets using the same type of processor built by other firms.

It added that the Intel-based versions would be offered with either 64GB or 128GB of storage and would have price tags comparable to ultrabook laptops.

Different chipsets

One tech analyst told the BBC that other hardware makers were likely to feel aggrieved by the news.

"Microsoft can offer a competitive price for these specifications as it doesn't need to pay itself a licence for the Windows 8 software which other manufacturers will have to do, and that might make its PC and tablet-making partners unhappy," said Carolina Milanesi, research vice president at the technology consultants Gartner.

She added that the firm appeared to have focused on a specific part of the market which wanted a more powerful device than the iPad.

"They seem to be be targeting a professional audience," she said.

"So they are going head-to-head with Apple within the corporate sector. Price will be key - these devices won't be at the bottom end of the market. They will probably let other manufacturers fight over that space."

By contrast the tech research firm Forrester said it thought the focus for ARM-based Surface tablets would be consumers, rather than the enterprise sector.

But one of its analysts warned there was a risk customers would shy away if they found it confusing distinguishing between the two types of Windows 8 experience. This will be the first time Microsoft will offer a version of its PC system designed for chips based on ARM's architecture.

"Microsoft will be its own worst enemy in this market,"blogged Sarah Rotman Epps.

"Consumers aren't used to thinking about chipsets. Choice is a key tenet of Windows, but too much choice is overwhelming for consumers. Apple gets this, and limits iPad options to connectivity, storage, and black… or white."

ARM's ambitions

Despite the potential for confusion, British chip designer ARM said it was "excited" by the news.

The firm's designs have already proved popular with smartphone makers, but Microsoft's support for its technology in Windows 8 offers it the potential to expand into a market dominated until now by Intel and AMD.

"This represents a significant milestone in Microsoft's journey to expand the support of the Windows operating system and embrace the ARM architecture," said Lance Howarth, the firm's vice president of marketing.

"With the Surface for Windows RT announcement we are delighted to see yet another example of this partnership in action which follows on from various Windows RT devices demonstrated at Taiwan's Computex show recently."

Intel said it was also "pleased" about Microsoft's move.

"Intel believes in and supports an open and healthy ecosystem that delivers a broad scale of innovation and choice in solutions and user experiences," a statement said.

"We also believe Windows 8 on Intel architecture will deliver the most complete experience with the best performance and compatibility across all computing platforms."