Optimistic predictions of Vista adoption rates have again been put under scrutiny by research showing that half of the business PCs in the US don't meet Vista hardware criteria.

Desktops from 472 North American businesses were looked at by Softchoice Corp. Half of them didn't have enough hardware for the baseline version of Vista and 94 percent couldn't run Vista Premium.

The research authors suggest that business has extended PC hardware refresh cycles to five years or more to save cost. This now comes up against Vista hardware requirements which are said to be 243 percent more onerous in CPU horsepower terms than those of Windows XP.

Dean Williams of Softchoice said: "At the time of release 71 percent of the PCs met the system requirements for Windows XP, whereas only 50 percent of the PCs included in this study meet the minimum requirements to run Windows Vista."

This calls into question predictions such as those from IDC that 90 million copies of Vista will ship in 2007. This study was funded by Microsoft. An Ovum analyst went further and predicted up to 15 percent of Windows users will switch to Vista in its first year of availability.

In an executive email sent to customers Microsoft CEO Steve Ballmer said: "Windows powers 845 million computers." Fifteen percent of that equates to almost 127 million Vista shipments in year one. Microsoft itself has said twenty percent of PCs will be running Vista by the end of its first twelve months availability; that's nearly 171 million copies.

An Altiris analyst as well as Gartner have poured icy water on such claims.

The Softchoice research provides a solid base for agreeing with them. Vista shipments will crawl along as companies wait until a hardware refresh cycle takes place before upgrading to an operating system that, for many, delivers little extra value.

Softchoice's Williams said: "Most organizations planning to deploy Vista within the next two years will have a PC life cycle that is affected by these factors, which, taken together, present a significant operational and financial stumbling block if not planned for well ahead of time."