This excerpt taken from the NVDA 10-K filed Nov 29, 2006.
Inventory cost is computed on an adjusted standard basis (which approximates actual cost on an average or first-in, first-out basis). Inventory costs consist primarily of the cost of semiconductors purchased from subcontractors, including wafer fabrication, assembly, testing and packaging, manufacturing support costs, including labor and overhead associated with such purchases, final test yield fallout, inventory provisions and shipping costs. We write down our inventory for estimated amounts related to lower of cost or market, obsolescence or unmarketable inventory equal to the difference between the cost of inventory and the estimated market value based upon assumptions about future demand, future product purchase commitments, estimated manufacturing yield levels and market conditions. If actual market conditions are less favorable than those projected by management, or if our future product purchase commitments to our suppliers exceed our forecasted future demand for such products, additional future inventory write-downs may be required that could adversely affect our operating results. If actual market conditions are more favorable, we may have higher gross margins when products are sold. Sales to date of such products have not had a significant impact on our gross margin. Inventory reserves once established are not reversed until the related inventory has been sold or scrapped.