Clock Speed

• The Intel Core 2 Duo E6600, like other entries in the Core 2 Duo family of processors, has a slower clock speed--the rate at which a processor performs its functions--than the Pentium D 925. It is measured at 2.4 gigahertz (GHz), compared to the D 925's 3 GHz.
  
  

FSB Speed

• At the front side bus (FSB)--the main path for data transfer in a computer--the Pentium D 925 has a speed of 800 megahertz (MHz). The FSB speed of the Core 2 Duo E6600 is faster, at 1066 MHz.
  
  

Die and Transistors

• The Pentium D 925 is cast on two dies, each measuring 162 square millimeters and containing a total of 376 million transistors. By comparison, the Core 2 Duo E6600 is of a smaller and more concentrated design: a single die measuring 143 square millimeters and containing 291 million transistors.