Windows Division revenue reflected relative performance in PC market segments. We estimate that sales of PCs to businesses grew approximately 4% and sales of PCs to consumers decreased 1%. Excluding a decline in sales of netbooks, we estimate that sales of PCs to consumers grew approximately 5%. Taken together, the total PC market increased an estimated 0% to 2%. Relative to PC market growth, Windows Division revenue was negatively impacted by higher growth in emerging markets, where average selling prices are lower than developed markets, and the deferral of $540 million of revenue relating to the Windows Upgrade Offer.
Windows Division operating income decreased, due mainly to lower revenue and a $163 million or 10% increase in research and development expenses, primarily associated with the Windows 8 operating system.