Intel shipped the Core 2 Duo line of processors back in July, sending a shock wave through the PC industry. Almost overnight, performance enthusiasts who had been singing the praises of Athlon 64 X2 CPUs changed their tune. Today, message boards are full of posts bragging about how they pushed their E6300 CPUs to over 3GHz. It's hard to believe that at the start of 2006, Intel seemed like an also-ran in the CPU market.

Today, it's AMD that's struggling. Once seen as lean and swift compared to the aging Intel juggernaut, AMD is now looking somewhat anemic. The Sunnyvale, California CPU company isn't giving up the fight easily, however. AMD slashed prices of its own processors line when Intel launched Core 2, and the typical AMD system tends to be somewhat less expensive—if also lower-performing—than similarly configured Intel Core 2 systems. But price cuts have hurt AMD's margins, and the last thing the company wants is to become a second-tier supplier, as it was back in the days when it was perceived only as a second source for Intel-compatible CPUs.

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Intel still has something of the killer instinct it once had, that paranoia that ex-CEO Andy Grove proclaimed frequently. So today, Intel is launching the Core 2 Extreme Q6700 quad-core processor. Built using two Core 2 Duo dies, the QX6700 is essentially two dual-core CPUs in a single package. This allows it to look like a single processor, which is important for operating system licensing. Microsoft counts the sockets, not the number of cores, in Windows licensing.

We built a system using the QX6700 to see if two additional cores can really make a difference. The answer, as you might imagine, is mixed. In some apps, it makes a huge difference. In other applications, you'd barely notice. But before we dive into the performance details, let's talk semantics.—next: Not "Real" Quad-Core? >