(a) Purchase accounting adjustments: Purchase accounting adjustments consistent of the impact to revenues and cost of sales associated with adjusting deferred revenue and inventories of acquired companies to fair value. For deferred revenue, as is the case with our existing business, at the time of acquisition, the acquired business recorded deferred revenue related to past transactions for which revenue would have been recognized by the acquired entity in future periods as revenue recognition criteria were satisfied. However, purchase accounting rules require us to write down a portion of this deferred revenue to its then current fair value, which is equivalent to the cost to complete the outstanding obligations required to earn the deferred revenue plus a reasonable margin. Consequently, in post-acquisition periods, we do not recognize the full amount of this deferred revenue. When measuring the performance of our business, however, we add back non-GAAP revenue associated with deferrals for which no future obligations existed as well as obligations we assumed to provide maintenance or support to customers of the acquired business that were excluded as a result of these purchase accounting adjustments. We believe that the non-GAAP revenue disclosures enhance investors' ability to conduct period-over-period analyses of our results that reflect the full impact of the acquired business's results together with the results from our pre-existing products and services.
In addition, the non-GAAP financial results exclude the impact to cost of sales from the markup of inventories required by GAAP as part of the fair value adjustments required under purchase accounting for business combinations. This results from marking the acquired company's inventory to fair value at the time of acquisition. This charge is not factored into management's evaluation of potential acquisitions or our performance after completion of acquisitions, because it is not related to our core operating performance, and the frequency and amount of this type of charge can vary significantly based on the size and timing of our acquisitions. Excluding this data provides investors with a basis to compare the company against the performance of other companies without this variability.