Advanced Micro Devices said Friday that it will start shipping quad-core versions of its Opteron microprocessor in August and that it expects hardware vendors to follow in September with servers based on the new chips.

According to AMD, the quad-core Opterons will deliver a performance gain of 40 percent to 70 percent over its existing dual-core chips, depending on the application. And they will do so without consuming more power, said the company, which will come to market with its quad-core offering nine months after Intel released versions of its Xeon server chips with four processor cores.

The quad-core product line, code-named Barcelona, gets some of its performance improvements because AMD is using a 65-nanometer manufacturing process to build the new chips, versus 90 nanometers for its dual-core chips. In addition, the quad-core devices are being manufactured on a single die of silicon, which allows for faster and easier memory sharing, AMD said.

The new chips initially will ship in two versions with different energy-usage levels: a standard model that consumes 95 watts of power, and a lower-power edition that operates at 65 watts. AMD said the clock speed of the quad-core processors will range up to 2 GHz in the standard devices and be 100 MHz to 200 MHz slower in the reduced-power chips.

Additional processors will be released in this year's fourth quarter with faster clock-speed frequencies that eventually will reach 3 GHz, AMD said. It added that users who are running servers with dual-core Opteron chips will be able to easily move to the quad-core devices because the two processor lines have similar power usage characteristics and were designed to operate within the same "thermal envelope."

John Fruehe, AMD's worldwide market development manager for server and workstation products, said that the bulk of Opteron sales have always been for the standard-power chips but that customers increasingly are asking for better energy efficiency. Because of the demand, company officials wanted to make sure that the lower-power devices got to market quickly, Fruehe said.

Intel launched its quad-core Xeon processors last November and claims to have shipped more than 1 million of the devices, which were code-named Clovertown.

Nathan Brookwood, an analyst at research firm Insight 64, said more details need to be disclosed about the performance of AMD's quad-core processors, including benchmarking data and the real-world experiences of users, before much can be said about how they compare with Intel's Xeon 5300 line.

"AMD didn't give us enough information to make a definitive statement," Brookwood said. "They believe that at 2 GHz, their performance will be very competitive with Intel's Clovertown products. However, there is no data to back that up."

Moreover, Brookwood wondered what will happen "over the next few months as Intel introduces 45-nanometer versions of its current products." He said that he expects AMD to reach 3-GHz clock speeds by this time next year.