Want a Skype 10-way conference call?

The latest version of Skype's internet-calling software can host up to 10 users on a conference call but only if your PC has a dual-core processor from Intel, Skype and Intel announced on Wednesday.

Intel's Core Duo and Pentium D processors have been designated the mass conference-calling processor of choice for Skype 2.0, launched last month. The limit will remain at five callers for PCs using single-core chips and AMD's dual-core Athlon 64 chip, which some tests have shown outperforms Intel's dual-core chip.

Skype's software allows PC users to make free voice calls to other Skype users over the internet and to call mobile phones and landlines for a fee.

Dual-core processors are basically two processing engines crammed onto a single piece of silicon. The individual processor cores tend to run slower than the clock speeds achieved by single-core chips but a dual-core chip excels when confronted with two demanding tasks at once, such as scanning a PC for viruses while decoding a video stream.

Despite both AMD and Intel releasing dual-core chips to the market last May, Skype 2.0 software will allow 10-way conference calls only if it detects code specific to Intel's chips when the PC boots, said Rob Crooke, vice president of Intel's Business Client Group.

Intel approached Skype with its plan to optimise code on its chips for Skype's software so users would have a good experience while hosting a multi-person conference call, Crooke said. In recent years, Intel has increasingly touted its software development resources as a competitive advantage over AMD, which also trails Intel in the marketing budget category.

Other processors based on the x86 instruction set, such as AMD's chips or Via's, obviously will not come with the same optimised code found on Intel's chips. Intel and Skype announced a partnership at the Fall Intel Developer Forum last August to make sure Skype's products would run well on Intel's chips.

VoIP (voice over IP) conference calls are a compute-intensive undertaking. Skype's minimum system requirement of a 400MHz processor applies only to a single person-to-person VoIP call. Adding multiple users to that connection requires the PC to simultaneously host multiple sessions with those new users, which strains the processor, a Skype representative said.

By choosing to work exclusively with Intel, Skype is excluding technology that is arguably more powerful than Intel's. A series of benchmark tests conducted last year by Tom's Hardware gave an overall performance edge to AMD's dual-core chips but rated Intel's dual-core chips better in some multitasking situations.

AMD is gaining some market share at Intel's expense. Intel still dominates the market for desktop and laptop processors but AMD took several points of market share from Intel in the fourth quarter, according to Mercury Research and Current Analysis.

Skype did extensive performance testing before releasing this feature for Intel's chips, said Henry Gomez, general manager of Skype's North American operations. He declined to comment on whether the company tested Intel's dual-core chips against AMD's dual-core chips but said Skype was very satisfied with the performance of the Intel chips.

The 10-way calling feature will be exclusive to Intel's chips for a limited time, Gomez said. Skype is not releasing the time frame for the expiration of the exclusive agreement, he said.

An AMD representative did not immediately return a call seeking comment.

Tom Krazit writes for CNET News.com