Microsoft Corp. will finish work on Windows 8 this summer, setting the stage for personal computers and tablets with the operating system to go on sale around October, according to people with knowledge of the schedule.

The initial rollout will include devices running Intel Corp. and ARM Holdings Plc chips, making good on Microsoft's promise to support both standards, said the people, who declined to be named because the plans are confidential. In embracing ARM technology, Microsoft is using the same kind of processors as Apple Inc.'s iPad. Still, there will be fewer than five ARM devices in the debut, compared with more than 40 Intel machines.

The timing would let Microsoft target Christmas shoppers with the new software, which works with touch-screen devices as well as laptops and desktop PCs. The Redmond, Washington-based company, which hasn't announced timing for the Windows 8 release, aims to take back sales lost to the iPad and reinvigorate the sluggish PC market. Apple released the third version of the iPad this month, posing an even stiffer challenge to Microsoft.