Marketable Securities

All of our cash equivalents and marketable securities are classified as “available-for-sale” securities. These securities are reported at fair value with the related unrealized gains and losses included in accumulated other comprehensive income, a component of stockholders’ equity, net of tax.

We performed an impairment review of our investment portfolio as of October 30, 2011. Based on our quarterly impairment review and having considered the guidance in the relevant accounting literature, we did not record any other than temporary impairment charges during the first nine months of fiscal year 2012. We concluded that our investments were appropriately valued and that no other than temporary impairment charges were necessary on our portfolio of available for sale investments as of October 30, 2011. The following is a summary of cash equivalents and marketable securities at October 30, 2011 and January 30, 2011:



	October 30, 2011
	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
	(In thousands)
Debt securities of United States government agencies	$	607,828	$	1,134	$	(330	)	$	608,632
Corporate debt securities	1,105,438		2,840		(531		)	1,107,747
Mortgage backed securities issued by United States government-sponsored enterprises	141,189		5,005		(31		)	146,163
Money market funds	36,296							36,296
Debt securities issued by United States Treasury	430,233		2,019		(505		)	431,747
Total	$	2,320,984	$	10,998	$	(1,397	)	$	2,330,585
Classified as:
Cash equivalents								$	149,047
Marketable securities								2,181,538
Total								$	2,330,585



	January 30, 2011
	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
	(In thousands)
Debt securities of United States government agencies	$	531,789	$	1,034	$	(226	)	$	532,597
Corporate debt securities	925,226		3,354		(208		)	928,372
Mortgage backed securities issued by United States government-sponsored enterprises	140,844		4,599		(21		)	145,422
Money market funds	132,586		—		—			132,586
Debt securities issued by United States Treasury	435,091		1,939		(18		)	437,012
Total	$	2,165,536	$	10,926	$	(473	)	$	2,175,989
Classified as:
Cash equivalents								$	350,787
Marketable securities								1,825,202
Total								$	2,175,989

The amortized cost and estimated fair value of cash equivalents and marketable securities which are primarily debt instruments are classified as available-for-sale at October 30, 2011 and January 30, 2011 and are shown below by contractual maturity.



	October 30, 2011				January 30, 2011
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Less than one year	$	1,236,291	$	1,237,962	$	1,176,046	$	1,178,733
Due in 1 - 5 years	984,387		988,574		899,993		904,926
Mortgage-backed securities issued by government-sponsored enterprises not due at a single maturity date	100,306		104,049		89,497		92,330
Total	$	2,320,984	$	2,330,585	$	2,165,536	$	2,175,989

Net realized gains for the three and nine months ended October 30, 2011 were $0.1 million and $0.5 million, respectively. Net realized gains for the three and nine months ended October 31, 2010, were $0.3 million and $1.3 million, respectively.