Quad Core Intel Xeon 53xx Clovertown
 

The Xeon 5160 (a.k.a. Woodcrest) is probably the best server chip Intel has made in the past decade. It delivers high IPC, high (3GHz) clock speed and a surprising low 80W TDP for a dual core design. But Intel's engineers saw that the fastest Woodcrest could score twice for Intel, in a slightly different form... or should we say package. Lower the voltage of a 3GHz from about 1.21 V to slightly less than 1.1V and you can only achieve 2.33GHz. However by running at 2.33GHz and 1.1V, Intel was able to cut the TDP in half. Now place two of these low voltage Xeons in one package and you get a 2.33GHz quad core Xeon and an 80W TDP. This is the essence of the CPU that bears the codename "Clovertown".

http://www.anandtech.com/IT/showdoc.aspx?i=2897