The valuation of inventory requires us to estimate obsolete or excess inventory as well as inventory that is not of saleable quality. The determination of obsolete or excess inventory requires us to estimate the future demand for our products. The estimate of future demand is compared to work-in-process and finished goods inventory levels to determine the amount, if any, of obsolete or excess inventory. As of December 29, 2012, we had total work-in-process inventory of $2.2 billion and total finished goods inventory of $2.0 billion. The demand forecast is included in the development of our short-term manufacturing plans to enable consistency between inventory valuation and build decisions. Product-specific facts and circumstances reviewed in the inventory valuation process include a review of our customer base, the stage of the product life cycle of our products, consumer confidence, and customer acceptance of our products, as well as an assessment of the selling price in relation to the product cost. If our demand forecast for specific products is greater than actual demand and we fail to reduce manufacturing output accordingly, we could be required to write off inventory, which would negatively impact our gross margin.

To determine which costs can be included in the valuation of inventory, we must determine normal capacity at our manufacturing and assembly and test facilities, based on historical loadings compared to total available capacity. If the factory loadings are below the established normal capacity level, a portion of our manufacturing overhead costs would not be included in the cost of inventory; therefore, it would be recognized as cost of sales in that period, which would negatively impact our gross margin. We refer to these costs as excess capacity charges. In the fourth quarter of 2012, excess capacity charges were $480 million. In the previous 11 quarters, excess capacity charges were less than $50 million in each quarter.