The PC industry is awash with rumours that PC vendors will start shipping machines with free upgrade coupons for Vista. The speculation has been intensified by unusual buying patterns for motherboards.

There is some historical substance behind the rumours. Microsoft and some PC vendors have offered such vouchers in the past. For example, when Windows XP came out in 2001, eMachines offered consumers a coupon for a free upgrade to the OS if they bought a compatible desktop ahead of the launch.

A few years earlier, Microsoft gave out a "technological guarantee" coupon for a free upgrade to Office 97 to purchasers of its Office for Windows 95 shipped during the third quarter of its fiscal 1997.

Behind the Vista coupon rumours is a fear in the PC industry that users might put off buying a new computer until Vista comes out next year.

Ever since Microsoft announced there would be a delay in shipping the OS, the PC industry has sought ideas on how to keep demand for new computers from flagging in the last few months of this year, the important Christmas buying season.

According to investment bank Goldman Sachs, unusual motherboard sales patterns support the idea.

The company cited a Taiwanese news agency's story on free Vista upgrade coupons as a possible reason that demand for motherboards in the clone market is stronger than demand in the brand name market.

Brand name PC vendors could be waiting to order more motherboards until later in the year, closer to October, the time when free Vista upgrade coupons might be bundled with new computers, Goldman said.

A few news reports (including this one) detailing plans for a Vista coupon have also floated across the Internet recently.

The story cites analysts attending an investor conference at contract notebook PC maker Compal Electronics on Wednesday, as saying that the company's CEO Ray Chen revealed plans for a free Vista upgrade coupon to be handed out with PCs sold later this year, most likely in October. But Compal denied the report.

"Our CEO said our customers, the brand name computer companies, will offer promotion programmes to stimulate market demand. He also said laptops compatible with Vista will be available in October or November, but he did not say anything about a voucher for a Vista upgrade," said Chih-ming Chang, a public relations officer at Compal Electronics.

Compal is one of the world's largest contract manufacturers of notebook PCs. The company counts Dell and HP as major customers.