As we reported earlier, AMD has added a triple-core variant of its upcoming Phenomdesktop processor to its CPU roadmap for 2008.

Read: AMD plans triple-core Phenom chip

What's the big deal?

Due out in the first quarter of next year, the triple-coreCPU will join dual and quad-core members of the Phenom family, known as the X2and X4 respectively. Unless Intel responds in kind, the new Phenom will be the onlytriple-core PC processor on the market.

AMD has yet to divulge full specifications and clockspeedsfor the new chip. But we do know it will mirror other members of the Phenomfamily with 512k of L2 cache memory per core, plus a 2MB pool of shared L3cache.

Likewise, detailed pricing has not yet been released. However,it seems logical that it will drop somewhere between the entry-level X2 and flagship X4models.

All of which leaves the simple question, why? The mostobvious answer involves production yields.

Quad core (minus one)

Specifically, the new triple-core chip is not thought to be basedon a separate processor die. Instead, it's a full quad-core chip with one ofits execution cores disabled. In other words, this triple-core model will allowAMD to salvage a few of those quad-core processor dies that come back from itsfabs with one broken core.

A related explanation is simply that AMD can do this, while Intelcannot. Or at least not as easily. Intel's current quad-core chips, of course,are constructed using a pair of dual-core CPU dies crammed together into a singleprocessor package. Dual dual-core, if you like.

It would not be impossible for Intel to ship a triple-core CPUusing its current multi-die approach. But it's hard to see how the resulting processorwould avoid suffering from an imbalance of resources.

The triple-core chip is undoubtedly an attempt by AMD to gain a competitiveadvantage over its rival.

A desperate move by AMD

Early benchmarks of AMD's new Opteron quad-core server processorhave been disappointing. In a direct fight - dual vs dual and quad vs quad - ittherefore looks likely that the closely related Phenom desktop CPU willstruggle to match Intel's existing 65nm quad-core chips.

The release of Intel'sfancy new 45nm quad-core processor later this year will only make mattersworse.

All of which means that the triple-core Phenom is probably a rather desperateattempt by AMD to win a few benchmark contests. If priced to compete with certaindual-core models in Intel's Core 2 range, triple-core Phenom will surelydeliver some impressive performance numbers. In multi-threaded andmulti-tasking work loads, at least.

Of course, one or two of the more cynical attendees at the current IntelDeveloper Forum tech fair, which has just kicked off in San Francisco, have other ideas. They reckonthe triple-core announcement is merely designed to ruin the vibe for Intel'sbig announcements later this week.

Whatever the reason, triple-core Phenom will be anintriguing distraction for budget-conscious PC buyers.

(For the record, AMD says the first quad-core Phenom desktopchips will go on the sale before the end of 2007.)