Acer president Gianfranco Lanci became the first major PC manufacturer to openly attack Microsoft over the Windows Vista operating system in the Financial Times Deutschland on Monday.
Lanci said the operating system was riddled with problems and gave users and businesses no reason to buy a new PC, according to the report. Taiwan-based Acer is the world's fourth-largest PC manufacturer, after HP, Dell and Lenovo.
"The whole industry is disappointed with Windows Vista," Lanci said.
Despite the long wait between Windows XP and Vista, the latest operating system still lacks maturity, he said. "Stability is certainly a problem," he said.
Users are voting with their feet, Lanci said, so that the Vista launch has had the smallest impact on PC sales of any version of Windows in the history of PC manufacturing. He added the situation didn't look likely to change in the next six months.
Many business customers have specifically asked for Windows XP to be installed on their new machines, Lanci noted.
While industry pundits have detailed user problems with Vista over the past few months, including sluggishness, the expense of acquiring hardware powerful enough to run the OS and lack of support for many critical applications, PC makers have so far looked on the brighter side.
HP, Dell, Lenovo and Toshiba have continued offering XP-equipped machines, but these are generally aimed at consumers or small businesses, not large corporate clients.
Microsoft itself says Vista has been a smashing successs, saying it had already sold 20 million Vista licences by March.
Last week the company said its quarterly income was $13.4 billion ($6.5 billion), up 13 percent from the same quarter last year, growth it said was partly due to strong Vista sales.
The company has said most Vista users are satisfied and that nearly all software and hardware is compatible.
On the other hand, the company recently told analysts it expects Windows XP to make up a significantly larger part of sales than it had previously expected, at Vista's expense.
Chief financial officer Chris Liddell has told analysts that he expects XP to make up 22 percent of sales in Microsoft's new fiscal year, up from the previous estimate of 15 percent. Vista would make up the remaining 78 percent of Windows sales. Windows XP sales will, in other words, be nearly 50 percent higher in the next 12 months than Microsoft had estimated earlier.
Michael Cherry, analyst with Directions at Microsoft, said part of the problem is that users prefer lower-cost machines that might not work well with Vista.
"Most of the machines I see pitched in catalogues are in the $700 range, certainly under $1,000," said Cherry. "Computers with that amount of hardware are a better fit for XP. With Vista's requirements, people may be thinking about sticking with XP, and putting less money into the hardware."
It's possible, Cherry added, that Microsoft might find itself forced to recognise more reality in the future. "At some point, they might have to consider limiting the availability of XP," to push people to Vista.
The software developer has made at least one move in that direction already. In mid-April, it announced it would terminate sales of Windows XP to resellers and retail after January 2008. User reactions were almost unanimously negative.
Gregg Keizer of Computerworld contributed to this report.