This excerpt taken from the HPQ 10-K filed Dec 17, 2009.
Long-Lived Asset Impairment
HP evaluates property, plant and equipment and purchased intangible assets with finite lives for impairment whenever events or changes in circumstances indicate the carrying value of an asset may not be recoverable. HP assesses the recoverability of the assets based on the undiscounted future cash flow the assets are expected to generate and recognizes an impairment loss when estimated undiscounted future cash flow expected to result from the use of the asset plus net proceeds expected from disposition of the asset, if any, are less than the carrying value of the asset. When HP identifies an impairment, HP reduces the carrying amount of the asset to its estimated fair value based on a discounted cash flow approach or, when available and appropriate, to comparable market values.