The Windows PC market is contracting. The market data has been showing unit shipment declining for some time with the latest quarter having perhaps the steepest decline for two decades.
What remains undocumented however is how the market looks when considering economic value. A more complete picture would be to show revenues, average selling price (or revenue/unit), operating margins/unit and percent of profit capture.
The data is not beyond reach however. It involves combining the shipment estimates from e.g. Gartner with financial reports from the companies themselves. Some analysis is required to estimate margins but they are also not hard to obtain (e.g. from third parties.)
So here is a view of the market for the fourth quarter 2012:



