The quad-core chips that have sat atop the microprocessor heap for the past two years are about to start being replaced by bigger, burlier six-core processor technology.

In a keynote address at Intel's annual developer forum last week in San Francisco, Patrick Gelsinger , senior vice president and general manager of the chip maker's digital enterprise group, announced that a six-core Xeon server processor will ship in September.

Code-named Dunnington, the X7460 Xeon chip is built with Intel's 45-nanometer Penryn technology.

Moving beyond quad-core processors is a major step -- and one that keeps Intel well ahead of rival Advanced Micro Devices Inc. , said Dan Olds, an analyst at Gabriel Consulting Group.

"This is a big deal," said Olds. "What we don't know is how much power the chips consume and how much heat they will dissipate, and those are key concerns."

AMD isn't slated to release its first six-core chip, code-named Istanbul, until the second half of 2009.

Intel executives last week also disclosed that the first offering in the new Nehalem processor family, a quad-core server chip, is expected to ship this fall. The other members of the Nehalem family -- desktop, dual-core, eight-core and additional quad-core chips -- are slated to ship over the next year.

Jim McGregor, an analyst at In-Stat, said the lengthy rollout schedule could indicate that the technology is more complex than Intel engineers had expected.