Windows Division revenue increased from the prior year, due in part to the recognition of a net $622 million of revenue related to Windows Deferral, as well as due to sales of Surface and Windows 8 upgrades. OEM revenue grew 17%, reflecting the net Windows Deferral recognition and increased demand in our distribution channels, offset in part by a decline in the x86 PC market.
Windows Division operating income increased, primarily due to revenue growth, offset in part by higher sales and marketing expenses and cost of revenue. Sales and marketing expenses increased $420 million or 49%, reflecting advertising costs associated with the launch of Windows 8 and Surface. Cost of revenue increased $293 million or 58%, including product costs associated with Surface and Windows 8 and Windows 8 upgrade support costs.