When first launched on November 17, 2008, Intel offered three Core i7 models based on the C0 core stepping. They followed this up with the new D0 core stepping on May 31, 2009. The first processors to feature the new D0 stepping was the Core i7-975 Extreme Edition, the Core i7-950 and the Core i7-920. This was followed up lately by the Core i7-960 on October 20, 2009.
Stepping is another word for a revision number. It is basically a way for microprocessor manufacturers to designate "steps" in the evolution of their microprocessor designs. Instead of using a revision number (1.1 -> 1.2), they use a combination of a letter and a number (B0 -> B1). So what's the big deal about core steppings? Read on and find out! Read more at TechARP.