U.S. computing giant Microsoft (IW 500/15) posted Thursday lower earnings and revenues for its fiscal first quarter, citing the slowdown in the personal computer market.

Microsoft said net profit fell 21% from the year-ago quarter, to $4.5 billion, nevertheless topping Wall Street estimates.

Earnings per share excluding exceptional items were 65 cents, well above the average estimate of 56 cents.

Revenue fell 8% in the 2013 first quarter that ended Sept. 30, to $16 billion, as sales fell ahead of the release of its new Windows 8 operating system, next week.

$1.36 Billion Deferred

Offers of Windows upgrades, pre-sales of Windows 8 to computer builders and hardware manufacturers, and an upgrade offer on its new Office meant a deferral of $1.36 billion of revenue and 13 cents of diluted earnings per share, the company said.

"The launch of Windows 8 is the beginning of a new era at Microsoft," said Steve Ballmer, Microsoft's chief executive.

"Investments we've made over a number of years are now coming together to create a future of exceptional devices and services, with tremendous opportunity for our customers, developers, and partners."

The Redmond, Wash.-based company will release its new Surface tablet computer -- running on Windows 8 and designed to challenge Apple's iPad -- on Oct. 26.

"While enterprise revenue continued to grow and we managed our expenses, the slowdown in PC demand ahead of the Windows 8 launch resulted in a decline in operating income," said Peter Klein, Microsoft's chief financial officer.