1 assets when the fair value is obtained from real time quotes for transactions in active exchange markets involving identical assets.  Our available-for- sale securities are classified as having Level 2 inputs.  Our Level 2 assets are valued utilizing a market approach where the market prices of similar assets are provided by a variety of independent industry standard data providers to our investment custodian.  Most of our cash equivalents and marketable securities are valued based on Level 2 inputs.  We do not have any investments classified as Level 3 as of January 26, 2014.



All of our available-for-sale investments are subject to a periodic impairment review. We record a charge to earnings when a decline in fair value is significantly below cost basis and judged to be other-than-temporary, or have other indicators of impairments.  If the fair value of an available-for-sale debt instrument is less than its amortized cost basis, an other-than - temporary impairment is triggered in circumstances where (1) we intend to sell the instrument, (2) it is more likely than not that we will be required to sell the instrument before recovery of its amortized cost basis, or (3) a credit loss exists where we do not expect to recover the entire amortized cost basis of the instrument. If we intend to sell or it is more likely than not that we will be required to sell the available-for-sale debt instrument before recovery of its amortized cost basis, we recognize an other-than- temporary impairment in earnings equal to the entire difference between the debt instruments’ amortized cost basis and its fair value.  For available-for-sale debt instruments that are considered other-than-temporarily impaired due to the existence of a credit loss, if we do not intend to sell and it is more likely than not that we will be required to sell the instrument before recovery of its remaining amortized cost basis (amortized cost basis less any current-period credit loss), we separate the amount of the impairment into the amount that is credit related and the amount due to all other factors.  The credit loss component is recognized in earnings.

 

Stock-based Compensation



We measure stock-based compensation expense based on the estimated fair value of equity awards at the grant date, and recognize the expense using a straight-line attribution method over the requisite employee service period. We estimate the fair value of employee stock options on the date of grant using a binomial model. We use the closing trading price of our common stock on the date of grant, minus a dividend yield discount, as the fair value of awards of restricted stock units, or RSUs. The fair value of our employee stock purchase plan is calculated using the Black-Scholes model.  Our stock-based compensation for employee stock purchase plan is expensed using an accelerated amortization model.

We determine the fair value of stock option awards on the date of grant using an option-pricing model that is affected by our stock price as well as assumptions regarding a number of highly complex and subjective variables. These variables include, but are not limited to, weighted average expected