On Monday, Apple ended its transition to Intel-supplied chips with a bang, replacing its Power Mac desktops with the Mac Pro.

This high-end desktop runs on two dual-core Xeon chips at speeds ranging from 2GHz to 3GHz; more important, the chip's ability to deliver more performance per watt means that Apple can replace the cooling systems included in its G5-based desktops with more features such as drive bays.

But what does that really mean for Mac users? And is this new Intel-based desktop that much of an improvement over its PowerPC-based predecessor? To get to the bottom of these and other questions, we've spent the time since the Mac Pro's unveiling poring over Apple's Web site, press releases, and technical documents, not to mention taking a visit down to Cupertino to familiarize ourselves with the ins and outs of Apple's latest professional desktop.

The dimensions of the Mac Pro case are exactly the same as those of the Power Mac G5. But there are still a few external differences between this new Intel machine and the G5 that are worth noting. On the front of the Mac Pro's case, you'll notice that there are now two optical drive bays (for the first time on a Mac since the final Power Mac G4 model, released in 2003). Lower down, Apple has added two ports on the front panel: a second USB 2.0 port and a second FireWire port, this one of the FireWire 800 variety. Meanwhile, on the back, Apple has moved the power supply to the top, replaced the two airflow vents with a single vent, and reorganized the rear ports into a smaller area next to the vent.

Inside Apple's new Mac Pro

On the inside, the Mac Pro is almost completely different from the Power Mac G5. But since this is the last portion of the Mac product line to make the jump to Intel processors, let's start with them: The Mac Pro uses the Xeon 5100, the newest processor in Intel's server-level arsenal (codenamed 'Woodcrest'). As with previous Power Macs, and every Intel Mac save the Core Solo Mac mini, the new Xeon processor is a dual-core processor, with two brains on the same piece of silicon. Unlike the Core Duo line of processors, which can only work alone, the Xeon processor is made to work in groups -- making it the ideal chip for use in these new quad-core systems. Although the high-end configuration of the final Power Mac G5 model did come in a quad-core version, the rest of that line was powered by a single dual-core G5 chip. In contrast, the entire Mac Pro line has two dual-core processors, spreading quad-core power throughout the line.

Unlike in the past, Apple isn't offering three models with different specs and price points, nor is it limiting certain features of the Mac Pro to high-end configurations as it did with portions of the Power Mac line. Instead, Apple offers one "suggested configuration" of the Mac Pro that sells for £1,445 ($2,499 in the US). All UK prices in this article are exclusive of VAT. This configuration includes two 2.66GHz dual-core Xeon processors, 1GB of RAM, an nVidia GeForce 7300 GT graphics card with 256MB of GDDR2 SDRAM, a 250GB hard drive, and a 16x SuperDrive. For comparison purposes, the quad-core Power Mac that the Mac Pro replaces cost from £1,956 ($3,299). That machine had a slower processor, less L2 cache, and a slower frontside bus; other specs like the hard drive capacity and optical drive are the same.)

 border=0 /><BR></div>
Although there

But no matter how you configure a Mac Pro, there are still a few constants: every model includes 4MB of shared L2 cache per processor and two 1.33GHz system buses, one per processor.

We'll leave the exercise of recreating the five million or so configurations to the reader. But we can tell you that upgrading to the 3GHz processors will bump up the price tag by £460 plus VAT ($800), while opting for two 2GHz Xeons will save you £170 ($300) off the base configuration price. Adding memory will cost you anywhere from £170 ($300) for 2GB of installed RAM to £3,270 ($5,700) if you max out the machine to 16GB. Additional 500GB hard drives for the Mac Pro's four drive bays cost £230 ($400) each.

Since pro customers typically customize their systems when ordering, Apple seems to have picked one middle-of-the-road model (albeit a powerful one) to standardize on. But as Apple representatives told us, Mac resellers and even Apple retail stores can order the models from Apple that they think will be most popular -- essentially leaving the configuration choices up to them. And of course, individuals can use the suggested configuration as a starting point, and build up (or down) as needed.

Memory tricks

While the DDR2 RAM in the Mac Pro is the same speed as that in all other current Intel Macs (667MHz, compared to the Power Mac G5's 533MHz), the Mac Pro uses Fully Buffered Memory modules, or FB-DIMMs. Each FB-DIMM has built-in error checking and correction, and carries a chip (known as an Advanced Memory Buffer, or AMB) that controls data transmission.

As a result of the AMB chip on every RAM module, each Mac Pro DIMM comes complete with its own heat sink. Apple says that by attaching a heat sink to every module in order to dissipate heat, it can keep fan noise to a minimum. Apple says it's provided a thermal specification for the modules to the companies that are manufacturing Apple-branded RAM for these systems. Since they can come from different manufacturers, RAM modules may vary in appearance depending on how their manufacturer chose to meet Apple's specs. Apple's also pushing for its thermal specification to be adopted as a standard by the JEDEC standards body, which would make it easier for third-party RAM vendors to manufacture heat-sinked RAM to meet the needs of Mac Pro users.

The Mac Pro has two small riser cards, each of which contains four FB-DIMM slots. To install RAM, you slide a riser card out and set it down on a flat surface. (The bottom of the riser card contains plastic feet so that the circuit board itself doesn't make contact with the surface to place it on.) Then you install the memory modules -- always in pairs of the same capacity from the same manufacturer. You need to install pairs of RAM in the proper order, which is printed on the inside of the G5 door: a pair in the top two slots of the top riser, then in the top two slots of the bottom riser; then in the bottom two slots of the top riser; and finally in the bottom two slots of the bottom riser. When you're done installing RAM, you slide the riser card or cards back into the Mac Pro until they re-connect with the motherboard.

Apple includes two 512MB modules in the stock configuration. As with the Power Mac, the Mac Pro requires matched pairs of RAM to function. To max out the RAM, you'd need to install 2GB modules in each of the Mac Pro's eight RAM slots. That's a lot of RAM.

 border=0 /><BR></div>
We won

The Mac Pro uses second-generation SATA drives with a maximum throughput of three gigabits per second (sometimes referred to as SATA II). Actual throughput is much less, however, limited by the speed of the drives themselves. Power Macs also used SATA drives, but the slower 1.5GBps variety. Those older drives will, however, work fine in the Mac Pro.

Each Mac Pro hard drive is mounted on a metal drive chassis with four screws. The chassis slides into place, attaching directly to the Mac Pro's motherboard. There are no cables to attach. (Although this method seems similar to the method Apple's Xserve uses to attach drives, it's not really comparable: the Xserve's drives are hot swappable and include status lights; these drives can only be swapped when the Mac Pro is shut off, and the drive chassis are simply metal, with no special lights or other electronics.

There's room for up to four drives, two more than in the Power Mac G5. Apple hasn't managed to squeeze more than two hard drives into a desktop Mac since the days of the Power Mac G4, so this is a welcome addition. Apple says you can install up to 2TB (that's terabytes, folks -- a thousand gigabytes!) of internal storage -- the biggest drives the company sells are 500GB -- but the new 750GB SATA drives on the market actually increase that total to 3TB. Best of all, with space for so many drives, you can easily set up an internal RAID for faster storage or mirrored backup, or even set aside a spare drive for use with Leopard's forthcoming Time Machine backup utility.

Power savers

One of the biggest benefits of switching to Intel processors is that they use less energy and, therefore, generate much less heat than the PowerPC processors Apple was using previously. Less heat produced means less cooling required, so by removing fans and other design elements implemented specifically to keep air flowing, Apple reclaimed a lot of space. Gone are the four separate air-flow conduits of the original G5, as well as the special molded-plastic interior door that kept air flowing even if you removed the G5's external door. And the two Xeon processors fit beneath a heat sink that's actually smaller than one of the dual-processor Power Mac G5's two heat sinks.

The Quad G5 used nine fans and a liquid cooling apparatus. The Mac Pro, on the other hand, has only four fans and no liquid cooling -- that should give some indication of the amount of cooling needed. We didn't notice any loud noise coming from Apple's demo Mac Pro, and Apple told us that the fans' dynamic range is very small, meaning you shouldn't experience large fan-noise spikes as with the Power Mac G5.

In theory, yes. Apple could shrink the case to make a smaller form factor -- but in doing so, the company would also have to remove things like the second optical drive bay, hard drive bays, and perhaps more. In short, Apple would have to completely redesign the Mac Pro, and for the customers who are most interested in buying one, the vast expansion options are most likely a large selling point. And from a business standpoint, it's worth asking: would such a system create new Mac buyers, or just siphon sales away from the Mac Pro and iMac?

Optical storage

Well, there are the two full-size optical drive spaces. And expansion cards are no longer quite as crowded as they once were: Previously, installing a high-end, double-sized graphics card took up not only the PCI Express slot meant for graphics, but also the slot next to it. That left users with two free PCI Express slots instead of three. With the Mac Pro, Apple has made the graphics slot able to accommodate a wide graphic card all by itself.

In the Power Mac, each PCI Express slot had a set bandwidth, expressed in terms of lanes -- the graphics slots was the fastest at 16x, with one 8x slot and two 4x slots as well. With the Mac Pro, Apple says that when you boot the computer after installing a new PCI Express card, the OS will let you choose the amount of bandwidth to dedicate to that slot. Apple told us that the total amount of bandwidth available to the PCI Express bus is less on the Mac Pro than on the Power Mac, but said the ability to direct that bandwidth as needed should make up for such a shortcoming. They also told us that there's more power (total wattage) available to the PCI Express bus, letting you power two ATI X1900 XT graphics cards (though not two nVidia Quadro FX 4500's, according to Apple).

If you need AirPort Extreme, Bluetooth, or both, you'll need to configure your Mac Pro to include those options. You can add Bluetooth for £17 ($29), AirPort Extreme for £26 ($49), or both together for £43 ($79).

For £60 ($100), Apple will add a second 16x SuperDrive to the Mac Pro. With two drives, you could burn a DVD Studio Pro project and rip an audio CD into iTunes at the same time, for example. And since the bays hold standard 5.25-inch drives, you can add a newer optical drive, such as one that supports the Blu-Ray high-definition DVD format, as prices drop.