66 (more specifically 66.667) megahertz (MHz) is a common divisor for the front side bus (FSB) speed, overall central processing unit (CPU) speed, and base bus speed. On a Core 2 CPU, and a Core 2 motherboard, the FSB is 1066 MHz (~16 × 66 MHz), the memory speed is usually 666.67 MHz (~10 × 66 MHz), and the processor speed ranges from 1.86 gigahertz (GHz) (~66 MHz × 28) to 2.93 GHz (~66 MHz × 44), in 266 MHz (~66 MHz × 4) increments.

The Green Bay Packers of the National Football League retired jersey number 66 for linebacker Ray Nitschke. The last Packer to wear number 66 before it was retired in 1983 to honor Nitschke was offensive tackle Larry Pfohl, who is better known to professional wrestling fans as Lex Luger.

Jersey number 66 was retired by the Pittsburgh Penguins of the National Hockey League in honor of Mario Lemieux.

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