increased reflecting the increased revenue and decreased research and development costs, partially offset by increased Windows Vista product costs and increased sales and marketing expenses for launch-related programs. The decrease in research and development costs reflects the capitalization of certain Windows Vista software development costs and completion of product development on Windows Vista. Headcount-related costs decreased 3%, driven by a 1% decrease in headcount and a decrease in stock-based compensation expense. 

 

Fiscal year 2006 compared to fiscal year 2005 

 

Client revenue increased reflecting $1.18 billion or 12% growth in OEM revenue driven by 17% growth in OEM license units from increased PC unit shipments, partially offset by a $118 million or 6% decrease in revenue from commercial and retail licensing of Windows operating systems. During the year, the OEM premium mix increased two percentage points to 52%. OEM revenue growth included an increase to revenue of $89 million resulting from the alignment of our billings associated with OEM distributors in our system builder channel with both industry standards and other Microsoft channels. 



Client operating income increased reflecting the increase in OEM revenue partially offset by a $224 million increase in sales and marketing expenses, excluding headcount-related costs, mainly driven by increased investments in partner marketing and Windows Vista pre-launch programs. Headcount-related costs increased 6%, driven by a 13% increase in headcount primarily associated with Windows Vista and further investments in our sales and marketing organization, and an increase in salaries and benefits for existing headcount, partially offset by a decrease in stock-based compensation expense. 

 

Server and Tools 

 

 

Server and Tools offerings consist of server software licenses and client access licenses (“CAL”) for Windows Server, Microsoft SQL Server, and other server products. It also includes developer tools, training, certification, Microsoft Press, Premier and Professional product support services, and Microsoft Consulting Services. Server and Tools concentrates on licensing products, applications, tools, content, and services that make information technology professionals and developers more productive and efficient. The segment uses multiple channels for licensing including pre-installed OEM versions, licenses through partners, and licenses directly to end customers. We sell licenses both as one-time licenses and as multi-year volume licenses. 

 

Fiscal year 2007 compared to fiscal year 2006 

 

Server and server application revenue (including CAL revenue) and developer tools, training, and certification revenue increased $1.12 billion or 14%. This increase was primarily driven by increased revenue associated with SQL Server, Windows Server, and Visual Studio. The results reflect broad adoption of Windows Server products, especially SQL Server which grew over 20%. Consulting, Premier, and Professional product support services revenue increased $404 million or 24% primarily due to higher demand for Premier services in corporate enterprises. Foreign currency exchange