In recent years, Intel has maintained two lines of processors, Pentium and Xeon. The former targeted desktops, while the latter focused on workstations. The two chips were architecturally similar, but the Xeon had a faster clock speed, front-side bus, and larger onboard cache, and could be configured into multiple-processor PCs.
A few years back, Intel introduced HT Technology, which stood for hyper-threaded. Chips with HT Technology contain components of two processors, but only one execution core. It's analogous to dual carburetors on a race car, which would accelerate performance, but only so much, since there's still just one engine. Ultimately, Intel added HT Technology to both Xeons and Pentiums.
Then came the first generation of dual core chips, which have two complete and separate processors in a single chip. The first generation of dual core Pentiums and Xeons were created by adding two current-generation processors to the same die, a process enabled by advancing manufacturing capabilities. The Xeon kept its moniker, while Pentium changed to Pentium D (for dual core).
Soon thereafter, Intel replaced the Pentium line with the Core 2 Duo and Core 2 Extreme, both dual core processors based upon a completely new processor architecture. Intel dropped the Pentium designation, presumably never to be seen again. Basically, the Duo and Extreme chips are the same, except that the Extreme chips have faster clock speeds and therefore run faster.
Interestingly, this is a matter of chip yield, not design. As you probably know, multiple processors are built on a single large wafer. After fabrication, all chips are tested for performance, which vary significantly across the wafer. "Alpha" chips become Core 2 Extreme chips that can be operated faster without burning them out. The "runts" are tossed in the Duo pile.
Intel has since shipped one new generation of Xeon, the 5100, and introduced another, both based on the same Core 2 Duo architecture, with the 7100 adding HT Technology to each processor core. Though these chips are also completely new architectures, Intel retained the Xeon brand—one can imagine to the befuddlement of brand and marketing experts worldwide. Like the Core 2 Duo, Xeons will be available at different clock rates, though the fastest Xeon will always be slightly faster than the fastest Core 2 Extreme.
How did these chips perform during testing? Well, the 2.93GHz Core 2 Extreme-based Dell Precision Workstation 390 that's the current alpha male in my office laid a serious whupping on every computer that I had ever previously tested. How bad? In MPEG-2 encoding, the 390 produced a 12-minute MPEG-2 file from Premiere Pro in 4:28 (min:sec) compared to 8:02 for a Dell Precision 670 workstation equipped with old-style dual 3.6GHz Xeons with HT Technology.
It also embarrassed a 3.4GHz Pentium D system configured with the first-generation dual core processor, which clocked in at 7:29. Performance gains in other programs like Sorenson Squeeze, Photoshop, and Acrobat were just as striking.
How did the Precision 390 stack up against a new dual Xeon? I tested against the HP xw8400 workstation that came equipped with 3.0GHz dual core Xeons (with no HT technology). In a perfect world, you would expect better than twice the performance, since it's two processors against one, and each was faster than the Core 2 duo in the Dell.
Here, however, performance was extremely application-dependent. For example, Premiere Pro produced the same MPEG-2 file in 4:02, faster than the 390 but only by about 10%. On the other hand, the 8400 was almost 33% faster than the Precision 390 on some large image Photoshop tests, and a whopping 100% faster on some 3ds max tests.
This reflects the reality that some tasks are more suited for or better at multithreading operation. The dual Xeon system will quickly pay for itself if you're working with a program like 3ds max that can immediately leverage the extra horsepower, but may not make sense for applications like Premiere Pro, at least in the short term.
Whichever processor you choose, buy the fastest model available. Though Intel claims that GHz no longer matters, that's only in comparisons with older style Pentiums. Within the Core 2 family, GHz still has a directly proportional effect on performance. For example, in my tests, the 2.93GHz Precision 390 was about 10% faster than a computer I tested from another vendor with a 2.67GHz processor, almost exactly the difference in GHz rating.
Buy a 1.86GHz model, and you might find only modest improvements compared to the fastest older-style dual Xeon or Pentium D systems.
Jan Ozer is the author of Adobe Digital Video How-Tos: 100 Essential Techniques with Adobe Production Studio, published by Peachpit Press (2006).