4. Intangible Assets

Intangible assets are carried at cost, less accumulated amortization, as disclosed in the following table (in thousands):

 

		September 24, 2011												December 31, 2010
		Gross Carrying Amount				Accumulated Amortization				Net				Gross Carrying Amount				Accumulated Amortization				Net
Existing and core developed technologies		$	52,694			$	(30,173	)		$	22,521			$	27,200			$	(26,747	)		$	453
Customer relationships			54,740				(9,656	)			45,084				3,700				(3,638	)			62
Purchase order backlog			4,260				(3,492	)			768				1,700				(1,700	)			—
Trade name			2,290				(2,290	)			—				—				—				—
Total amortizable intangible assets			113,984				(45,611	)			68,373				32,600				(32,085	)			515
In- process technology			16,270				—				16,270				—				—				—
Total intangible assets, excluding goodwill		$	130,254			$	(45,611	)		$	84,643			$	32,600			$	(32,085	)		$	515

The amortization expense was $5.4 million, and $1.6 million for the three months ended September 24, 2011 and September 25, 2010, respectively, and $13.5 million and $4.6 million for the nine months ended September 24, 2011and September 25, 2010, respectively. Expected future amortization for the fiscal years indicated is as follows (in thousands):

 

2011(Remaining months)		$	4,595
2012			15,307
2013			15,307
2014			15,307
2015			15,306
Thereafter			2,551
Total		$	68,373