Power Mac G5: The Next Generation

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Four years. That's how long Mac users have been staring at the fold-down door and the set of easy-to-grip plastic handles that enclose Apple's Power Mac G4. The outside of the machine hasn't changed much since its debut, in September 1999. And with the exception of incremental clock-speed boosts and occasional architectural tweaks, neither has the inside.

Now all that -- the Power Mac design and the computer inside it -- is history. We're entering a new Mac era, ushered in by a shiny metallic computer that houses a radically different system architecture. Here comes a new Power Mac to shake up the Mac world -- the G5. And given the forcefulness of Apple's claims about the G5's current and future speeds, this new aluminum desktop could set the entire computer industry on its ear.

The Systems

On the inside, the new Power Mac is different -- really different -- from the G4. But we realize that not everyone who needs the power of the G5 wants to know all the geeky details of microprocessors and memory buses. We'll dive into that stuff in short order, but first let's take a look at the tower that houses the Power Mac G5.

Like the current PowerBook G4s, the Power Mac G5 is sheathed in silvery metal. (As the iBook, iMac, and eMac are made of white plastic, we get the sense that Apple is making some pretty clear fashion statements about its professional and consumer products.) But this sheath isn't like any we've ever seen on a Mac: the aluminum on the front and back has more holes than a slice of Swiss cheese -- it's 35 percent air. The hundreds of tiny holes let air pass through, cooling the components within.

Cool Customer Cooling is vital in the G5 -- there are nine fans inside the box, which is split into four independent thermal zones. The reason? Apple knows that cooling components only while they're in use is more efficient than cooling every component at once. With a single thermal zone in a traditional machine, "everyone pays the price for cooling," says Jon Rubinstein, Apple's senior vice president of hardware engineering.

You might think that nine fans would make this Mac sound like a power blower (like the Xserve or the "Wind Tunnel" Power Mac G4s), but it's much quieter. The G5's intelligent fan management varies the fans' speed and cranks up the airflow in the appropriate zone only when things are heating up. The system is even smart enough to anticipate heat-generating work -- it can increase cooling before components get a chance to warm up.

If you're doing a lot of processing work, or if you're in a warm room, the inside of the G5 tower will definitely heat up faster, so the fans will crank up. But in normal operation, this system should be acceptably quiet. Apple claims that the Power Mac G5 runs at 35 decibels, compared with the mirrored-drive-door G4's 65 decibels, which created quite a ruckus. (To put those noise levels in context, a 70-square-foot office with lights, air conditioning, and a computer turned on registers at about 40 decibels.)

Everything and More Just about any port or plug we could think of has been included in the Power Mac G5. FireWire 800? Check. FireWire 400? Double-check: one on the back, plus a welcome one on the front, just below the power button. Our USB wish list included copious ports and the speed of USB 2.0, which is about 40 times faster than USB 1.1 (most Macs support USB 1.1). Again, the G5 delivers: two USB 2.0 ports live on the machine's back side, and a third resides on the front.

In terms of audio, the G5 covers both ends of the spectrum. For people who think small, there's a headphone jack on the front panel. If you think big, turn your attention to the optical digital audio-out port on the back. You can now connect a stock Power Mac to a home theater system and hear 5.1-channel digital surround sound. (Apple updated the DVD Player application on these systems to support 5.1 playback.) There's also an optical digital audio-in port for audio pros, as well as the old standby analog audio-in and -out ports.

The G5's metallic case creates one noticeable quirk: it effectively blocks radio signals, so the G5's optional $99 AirPort Extreme and $50 Bluetooth features are useless until you attach the included external antennas. Both of them -- the AirPort antenna is T-shaped, and the Bluetooth antenna is a cylinder -- plug into the back of the Mac. As with previous Power Macs, you can install an AirPort card later by sliding it in. The Bluetooth module's features are built in to the system's motherboard, so you've got to either opt for Bluetooth when you buy your system or use an external adapter later.

A Chip's Story

At the heart of the three Power Mac G5 models is IBM's new PowerPC 970 chip, which Apple has dubbed the G5. Several different chip models found their way into the Power Mac G4 line over the last four years, but none was enough of a leap forward to merit a new moniker or case design. However, this fifth-generation PowerPC chip is unlike any of the Motorola processors found inside the Power Mac G4.

The most noticeable difference between the G5 and the many G4 chips is clock speed: at 1.6GHz, 1.8GHz, and 2GHz, the three G5 chips are the fastest and most technically advanced that Apple has ever used.

What's more, when Steve Jobs unveiled the G5, he made a guarantee the likes of which Apple has never before offered:

In the next 12 months, the fastest G5 chip powering a Mac will run at a mind-bending 3GHz -- 50 percent faster than today's top model. Mac fans who have wondered whether Apple would ever again compete with Windows PCs can take heart. This is a changed Apple: the race to claim computer-speed supremacy is on.

Dreams of 2004's dual-3GHz Power Mac G5s aside, this G5 crop will undoubtedly answer the prayers of professional Mac users who need to process massive amounts of data as fast as possible. Adobe Photoshop pros, video editors, 3-D artists, and scientists will surely be first in line at their local Apple stores when these new Macs arrive in August.

New Chip Maker Back in the day, the PowerPC chip was a joint venture of Apple, IBM, and Motorola. But IBM and Motorola parted ways over the PowerPC. Motorola's G4 processor had a high-speed vector processing unit that sped certain tasks. IBM continued to supply Apple with G3 chips, but if you wanted that extra processing boost (which came to be known as Velocity Engine), you needed a G4 chip.

But anyone who's paid attention to the competitive world of desktop computers has noticed that as PC chip makers Intel and AMD have accelerated their chips to incredibly high clock speeds, the G4 has lagged behind. Lately, even Apple seemed to stop protesting that the gap was purely mathematical and not real.

Apple's search for a faster chip for its Power Mac line turned the company toward its other PowerPC partner. IBM specializes in incredibly fast processors designed for high-end computer workstations. The result is the G5, a chip that combines the processor core of IBM's high-powered Power4 chip with the familiar features that the PowerPC has brought to Power Macs -- including the Velocity Engine.

The Good Bits Apple trumpets the G5 chip as the world's first 64-bit microprocessor for a desktop computer. The differences between 64-bit chips and their 32-bit counterparts are stark but pretty geeky. The short version of the story is this: The G5 chip doesn't just have a high clock speed, measured in gigahertz -- it's also remarkably efficient, capable of performing numerous calculations simultaneously. This is why Apple claims that the chip is at least the equivalent of Intel's 3GHz and faster chips. Apple attaches this 64-bit chip to its new system architecture, which is faster than anything the company has ever created before. The Wintel side has had trouble moving to 64-bit chips, but Apple's new 64-bit computer doesn't require any updates to 32-bit applications before those programs can run on the new chip.

Mother of all Motherboards

If Apple had slapped a G5 chip into a Power Mac G4 chassis, the result wouldn't have been too exciting. The G5's heat output requires some extensive cooling work, and the Power Mac G4's innards aren't built to take advantage of the new chip's speed.

Feed It RAM The most important thing you can do to make a modern computer fast is to make sure the processor is continually fed data. From a processor's perspective, a hard drive is very slow -- for real speed, a processor must be fed by fast RAM.

The Power Mac G4 had three layers of cache RAM, speedy RAM designed to keep the processor fed with raw data so it could operate at peak efficiency. The G5 has two, but the third layer -- called Level 3 cache -- is gone. Believe it or not, that's not bad news. The Power Mac G5 can use regular system RAM, because that RAM connects to the processor at speeds far faster than any previous Mac model.

Speedy Connections At the heart of the Power Mac G5 is a frontside bus, the connection that links the processor with the system controller -- a special chip Apple designed to act as the computer's traffic cop, sending data to the processor, RAM, and other computer systems. The Power Mac G4's bus ran at 167MHz, so even with Double Data Rate (DDR) RAM, that system could feed the processor at only 1.3GB per second. The Power Mac G5's frontside bus runs at half the clock speed of its G5 processor, topping out at 1GHz for the top-of-the-line dual-2GHz model. In the dual-2GHz model, each G5 chip gets its own 1GHz connection, so the data flowing between one G5 chip and the system controller can't slow down the other chip.

The top two Power Mac G5 models use 400MHz DDR RAM -- that's speedy. But it gets better: the system uses two banks of that RAM simultaneously, combining two speedy RAM chips into one superspeedy RAM combo. (So you need to add RAM to the G5 in pairs, one module in the upper four-slot RAM bank, the other in the lower. If you use 1GB DIMMS, you can fill up all eight slots, for a staggering 8GB of RAM. The 1.6GHz G5, whose DDR RAM runs at only 333MHz, is limited to 4GB.)

The result: the G5 processor's connection to RAM can handle as much as 6.4GB per second. That translates to a massive speed boost for any data-intensive task.

If you do the math -- and we'll forgive you if you don't jump at the chance to multiply megahertz and gigabytes -- you'll find that the frontside bus can carry far more data than the G5 processor–RAM connection can at its top speed. That's OK, because the system controller also talks to the rest of the Power Mac's infrastructure -- the hard drive, video card, expansion cards, and other hardware that's carrying out high-impact tasks -- simultaneously inside the Power Mac's case. The upshot is that a large amount of data can move around the Power Mac G5 at once -- and that leads to speed.

Time for New Tech Other familiar technologies that populate Macs and PCs alike get a speed boost in the new Power Mac G5. The venerable PCI slots that Power Macs have sported since 1995 haven't been phased out, but they have been upgraded on the top two Power Mac G5 models with PCI-X slots, which accept most modern PCI cards (older cards that can't handle 3.3 volts won't work). If you install PCI-X cards into the slots, you'll see a major speed boost: one of the PCI-X slots runs at 133MHz, and the other two run at 100MHz. The 1.6GHz Power Mac G5 model has three old-style PCI slots running at the comparatively poky 33MHz.

The internal ATA hard drive has also been common in Macs since the mid-1990s, but the G5 has done away with the common parallel ATA standard and replaced it with serial ATA. Each Power Mac G5 can hold two serial ATA drives, each of which connects to the main system controller with a maximum data rate of 150MB per second -- not too shabby for hard drives, especially since the single superfast ATA bus on the Power Mac G4 had a maximum speed of 100MB per second. Serial ATA is also a much cleaner connection technology; the cables are simpler than the ribbons on parallel ATA drives, and Apple provides screws and snap-on cable connectors, so it's a breeze to install a drive without tools.

With serial ATA, you can connect only one drive per channel, as opposed to the two drives you could connect on parallel ATA buses. So you no longer have to worry about whether the new drive you're installing is jumpered to master or slave mode -- a very un-Mac-like experience to be sure. But the Power Mac G5 can connect to only two internal hard drives; the Power Mac G4 came with support for four internal drives, albeit at slower speeds.

The Last Word

After four years of minor improvements to Apple's flag-ship line, it was definitely time for a Power Mac revolution. With the G5, we've got one. Apple has upgraded almost every subsystem of the computer and engineered it for speed, starting with the fast processor at the heart of the box. The Power Mac G5 gives professional Mac users a good reason to upgrade -- and it shows that the Mac is still a strong competi-tor in the speed race with Intel-based PCs. Even Mac users who don't need the speed of these highly tuned professional machines can agree that having fast Macs that can compete -- both in real speed tests and in terms of raw gigahertz numbers -- with powerful PCs is a revolution whose time has come.

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