Financial Instruments

The following is a summary of cash equivalents and available-for-sale securities as of the end of the periods presented:



	June 30, 2012									March 31, 2012
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds	$	174,888	$	—	$	—		$	174,888	$	232,017	$	—	$	—		$	232,017
Bank certificates of deposit	189,914		—		—			189,914		159,972		—		—			159,972
Commercial paper	489,826		—		—			489,826		594,867		1		(1		)	594,867
Corporate bonds	207,372		3,713		(213		)	210,872		186,455		3,401		(184		)	189,672
Auction rate securities	32,250		—		(3,435		)	28,815		32,600		—		(3,671		)	28,929
Municipal bonds	19,598		677		(61		)	20,214		25,454		734		(28		)	26,160
U.S. government and
agency securities	668,759		382		(92		)	669,049		668,702		360		(149		)	668,913
Foreign government and
agency securities	228,947		1		—			228,948		249,951		—		—			249,951
Mortgage-backed securities	1,008,823		17,580		(2,193		)	1,024,210		878,842		15,094		(1,160		)	892,776
Debt mutual fund	40,500		—		(260		)	40,240		20,000		—		(219		)	19,781
	$	3,060,877	$	22,353	$	(6,254	)	$	3,076,976	$	3,048,860	$	19,590	$	(5,412	)	$	3,063,038

The following tables show the fair values and gross unrealized losses of the Company’s investments, aggregated by investment category, for individual securities that have been in a continuous unrealized loss position for the length of time specified, as of June 30, 2012 and March 31, 2012:



	June 30, 2012
	Less Than 12 Months					12 Months or Greater					Total
(In thousands)	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Corporate bonds	$	30,040	$	(122	)	$	1,782	$	(92	)	$	31,822	$	(214	)
Auction rate securities	—		—			28,814		(3,436		)	28,814		(3,436		)
Municipal bonds	2,271		(56		)	717		(5		)	2,988		(61		)
U.S. government and
agency securities	472,979		(92		)	—		—			472,979		(92		)
Mortgage-backed securities	224,250		(2,016		)	17,480		(175		)	241,730		(2,191		)
Debt mutual fund	40,240		(260		)	—		—			40,240		(260		)
	$	769,780	$	(2,546	)	$	48,793	$	(3,708	)	$	818,573	$	(6,254	)



	March 31, 2012
	Less Than 12 Months					12 Months or Greater					Total
(In thousands)	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Commercial paper	$	79,994	$	(1	)	$	—	$	—		$	79,994	$	(1	)
Corporate bonds	21,111		(184		)	—		—			21,111		$	(184	)
Auction rate securities	—		—			28,929		(3,671		)	28,929		$	(3,671	)
Municipal bonds	2,173		(24		)	366		(4		)	2,539		$	(28	)
U.S. government and
agency securities	460,735		(149		)	—		—			460,735		$	(149	)
Mortgage-backed securities	147,726		(1,040		)	15,923		(120		)	163,649		$	(1,160	)
Debt mutual fund	19,781		(219		)	—		—			19,781		$	(219	)
	$	731,520	$	(1,617	)	$	45,218	$	(3,795	)	$	776,738	$	(5,412	)

The gross unrealized losses on these investments were primarily related to failed auction rate securities, which was due to adverse conditions in the global credit markets during the past three years. The Company reviewed the investment portfolio and determined that the gross unrealized losses on these investments as of June 30, 2012 and March 31, 2012 were temporary in nature as evidenced by the fluctuations in the gross unrealized losses within the investment categories. Furthermore, the aggregate of individual unrealized losses that had been outstanding for 12 months or more was not significant as of June 30, 2012 and March 31, 2012. The Company neither intends to sell these investments nor concludes that it is more-likely-than-not that it will have to sell them until recovery of their carrying values. The Company also believes that it will be able to collect both principal and interest amounts due to the Company at maturity, given the high credit quality of these investments and any related underlying collateral.

The amortized cost and estimated fair value of marketable debt securities (bank certificates of deposit, commercial paper, corporate bonds, auction rate securities, municipal bonds, U.S. and foreign government and agency securities and mortgage-backed securities), by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations without call or prepayment penalties.



	June 30, 2012
(In thousands)	Amortized Cost		Estimated Fair Value
Due in one year or less	$	1,502,255	$	1,502,405
Due after one year through five years	303,951		308,085
Due after five years through ten years	253,312		257,837
Due after ten years	785,970		793,521
	$	2,845,488	$	2,861,848

Certain information related to available-for-sale securities is as follows:



	Three Months Ended
(In thousands)	June 30, 2012			July 2, 2011
Proceeds from sale of available-for-sale securities	$	97,571		$	30,377
Gross realized gains on sale of available-for-sale securities	$	787		$	339
Gross realized losses on sale of available-for-sale securities	(75		)	(5		)
Net realized gains on sale of available-for-sale securities	$	712		$	334
Amortization of premiums on available-for-sale securities	$	5,619		$	2,313

The cost of securities matured or sold is based on the specific identification method.