Although Intel has been using the Xeon name since the dualcore Xeon processors that power the Mac Pro and Xserve lines are entirely new chips based on Intel&;s bit Core architecture platform. This platform was initially introduced to the public late in with chips continuing to roll out throughout this year; it includes the Core Duo and Core Solo processors used in the Mac Mini and the iMac as well as some other chips that haven&;t shown up in Macs&;at least not yet.
Codenamed &;Woodcrest" the Xeon debuted at the end of June and was designed to offer topspeed computational throughput with better power efficiency than Intel&;s previous highend processors. The company terms it a &;server&; chip although most hardware vendors Apple included will use it in professional systems like the Mac Pro. That&;s due to the fact that the chip was designed to excel at the processing of huge amounts of data like those found in realworld applications like movie production with Final Cut Pro or image editing in applications like Aperture or Adobe Photoshop (once Photoshop is Intelnative on OS X).
The Xeon comes in three speeds: .GHz .GHz and .GHz. Like the Core Duo and IBM&;s PowerPC MP used in the current Power Mac G the has two microprocessor cores built into each chip. Both cores run at the same rated speed with a .GHz frontside bus (which connects the processor to the rest of the system) and share a MB Level cache which helps keep the processors humming during computeintensive tasks.
Unlike the cache in the Core Duo and PowerPC MP either processor core can utilize the entire cache if necessary which gives a performance boost in crucial dataprocessing tasks especially with legacy nonmultithreaded applications that aren&;t designed to take advantage of multiple processors.
One other reason aside from performance that the Xeon was the perfect chip to use in Apple&;s flagship Mac was because it is the only Core chip that can currently be used in a dualprocessor configuration similar to the Power Mac Quad G. The can only be used in single or dualprocessor configurations so we won&;t see any Xserves with four Xeons in it although Intel is expected to announce a quadcore successor to the series some time in .
How much better than a G?
In synthetic tests Apple claims that the GHz Mac Pro with its twin Xeon processors offers more than twice the integer performance of the previous top of the line the .GHz Power Mac Quad G and . times the floating point performance. Of course realworld benchmarks will tell the true story of the Mac Pro as it compares to its predecessor but the Xeon should have a distinct performance edge over the older PowerPC chip as we would expect in any more modern chip design with a faster frontside bus and larger and more flexible cache. (Each core in the PowerPC MP chip has MB of dedicated Level cache.)
But with the Xeon Intel claims that it has eliminated one huge performance advantage held by the PowerPC architecture: vector processing. Known to Mac users as AltiVec or the Velocity Engine this technology increased vectorbased processing significantly on the PowerPC machines and was one of the reasons that applications like Photoshop were able to manipulate such large image files with ease even when other parts of the Mac subsystem weren&;t as fast as comparable Intelbased PCs.
In the Core architecture Intel has a feature called Advanced Digital Media Boost. That may not roll off the tongue as cleanly as AltiVec but Intel claims that it achieves the same end. For Mac users the important thing to note about Advanced Digital Media Boost is that it executes bit vectorbased instructions in one clock cycle instead of the two clock cycles taken by previous Intel designs. This theoretically doubles the performance of vector operations and brings Intel to parity with AltiVec. It also should provide enhanced performance of native graphics applications especially when working with large amounts of data. (If you would like a much more indepth (i.e. geekier) explanation check out ArsTechnica&;s excellent analysis of the Core architecture written by Jon Hannibal Stokes.)
Intel and IBM don&;t use the same metrics or nomenclature when discussing power efficiency so it&;s hard to compare the true power efficiency of the Xeon series with the Power Mac G&;s PowerPC MP processor. The fact that Apple has been able to eliminate so much of the Power Mac&;s cooling apparatus says quite a bit about the power requirements of the however. Apple told us that the Mac Pro system as a whole only pulls watts versus watts for the Power Mac Quad G and a lot of that power is routed to the PCI Express bus.
The is only the beginning
The last two years have seen chip manufacturers push away from the &;speeds and feeds&; mentality of the previous decade largely a result of the fact that as chips have increased in speed their power consumption has increased as significantly. The result is that companies like Intel Advanced Micro Devices and IBM have moved to multicore designs that don&;t offer huge jumps in raw performance speed (as measured in gigahertz) instead providing tangible increases in performance (through multiple processor cores on a single chop) without linear increases in power consumption.
One of the great things for Mac users is that the Xeon used in today&;s Mac Pro is only the beginning of a line of highperformance chips that will be released in the next year&;as noted we should see quadcore chips as well as chips better tuned to run in portable systems and chips that offer notable increases in performance for lowend desktops.