Financial Instruments

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



	September 28, 2013									March 30, 2013
(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	$	168,053	$	—	$	—		$	168,053	$	108,311	$	—	$	—		$	108,311
Bank certificates of deposit	94,976		—		—			94,976		124,987		—		—			124,987
Commercial paper	582,348		—		—			582,348		503,550		—		—			503,550
Corporate bonds	299,100		2,823		(1,977		)	299,946		270,945		5,193		(135		)	276,003
Auction rate securities	25,150		—		(2,514		)	22,636		31,900		—		(3,200		)	28,700
Municipal bonds	28,592		371		(369		)	28,594		24,496		514		(70		)	24,940
U.S. government and
agency securities	924,072		401		(217		)	924,256		696,836		431		(45		)	697,222
Foreign government and
agency securities	319,960		—		—			319,960		269,901		—		—			269,901
Mortgage-backed securities	1,158,484		10,830		(12,640		)	1,156,674		1,180,156		17,601		(5,077		)	1,192,680
Debt mutual fund	61,350		—		(2,407		)	58,943		61,350		1,577		—			62,927
	$	3,662,085	$	14,425	$	(20,124	)	$	3,656,386	$	3,272,432	$	25,316	$	(8,527	)	$	3,289,221

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 September 28, 2013 and March 30, 2013:



	September 28, 2013
	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	$	127,859	$	(1,977	)	$	—	$	—		$	127,859	$	(1,977	)
Auction rate securities	—		—			22,636		(2,514		)	22,636		(2,514		)
Municipal bonds	9,691		(341		)	862		(28		)	10,553		(369		)
U.S. government and
agency securities	212,267		(217		)	—		—			212,267		(217		)
Mortgage-backed securities	610,583		(11,932		)	31,645		(708		)	642,228		(12,640		)
Debt mutual fund	58,943		(2,407		)	—		—			58,943		(2,407		)
	$	1,019,343	$	(16,874	)	$	55,143	$	(3,250	)	$	1,074,486	$	(20,124	)



	March 30, 2013
	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	$	27,114	$	(135	)	$	—	$	—		$	27,114	$	(135	)
Auction rate securities	—		—			28,701		(3,200		)	28,701		(3,200		)
Municipal bonds	8,927		(70		)	60		—			8,987		(70		)
U.S. government and
agency securities	388,696		(45		)	—		—			388,696		(45		)
Mortgage-backed securities	367,561		(4,930		)	11,029		(147		)	378,590		(5,077		)
	$	792,298	$	(5,180	)	$	39,790	$	(3,347	)	$	832,088	$	(8,527	)

The gross unrealized losses that had been outstanding for less than twelve months were primarily related to mortgage-backed securities, although the percentage of such losses to the total estimated fair value of the mortgage-backed securities was relatively insignificant. The gross unrealized losses that had been outstanding for more than twelve months were primarily related to failed auction rate securities, which was due to adverse conditions in the global credit markets during the past five years.

The Company reviewed the investment portfolio and determined that the gross unrealized losses on these investments as of September 28, 2013 and March 30, 2013 were temporary in nature as evidenced by the fluctuations in the gross unrealized losses within the investment categories. Additionally, in the past several years a portion of the Company's investment in the auction rate securities were redeemed by the issuers at par. Furthermore, the aggregate of individual unrealized losses that had been outstanding for twelve months or more was not significant as of September 28, 2013 and March 30, 2013. 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.



	September 28, 2013
(In thousands)	Amortized Cost		Estimated Fair Value
Due in one year or less	$	1,858,718	$	1,858,944
Due after one year through five years	384,528		385,905
Due after five years through ten years	252,551		254,235
Due after ten years	936,885		930,306
	$	3,432,682	$	3,429,390

As of September 28, 2013, $192.6 million of marketable debt securities with contractual maturities of greater than one year was classified as short-term investments. Additionally, the above table did not include investments in money market and mutual funds because these funds do not have specific contractual maturities.

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



	Three Months Ended						Six Months Ended
(In thousands)	September 28, 2013			September 29, 2012			September 28, 2013			September 29, 2012
Proceeds from sale of available-for-sale securities	$	104,021		$	119,058		$	199,160		$	201,163
Gross realized gains on sale of available-for-sale securities	$	266		$	1,042		$	1,367		$	1,829
Gross realized losses on sale of available-for-sale securities	(521		)	(12		)	(1,515		)	(88		)
Net realized gains (losses) on sale of available-for-sale securities	$	(255	)	$	1,030		$	(148	)	$	1,741
Amortization of premiums on available-for-sale securities	$	6,904		$	5,942		$	14,063		$	11,561

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