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Inside the G4 desktops

MacWorld Online

(IDG) -- Apple's new Power Mac G4 systems, introduced Tuesday during Steve Jobs' keynote, feature more than a faster G4 processor. Apple has thoroughly redesigned the desktop tower's motherboard, updating the memory controller and AGP slot, adding a PCI slot, revising the audio system and changing the location of the new CPUs, which range from 466MHz to 733MHz. Apple also updated the standard DVD-ROM or -RAM drive to a CD-RW drive in the 466MHz, 533MHz and 667MHz models, or Pioneer's new combination DVD-R/CD-RW drive in the 733MHz configuration. The 466MHz and 533MHz systems are available now; the faster versions are scheduled to ship in February.

The new chips

Officially, Apple describes the chips in its systems as the "PowerPC G4" without identifying the specific flavor. But examining the systems here at Macworld Expo, we saw that the 466MHz and 533MHz configurations use Motorola's PowerPC 7410, the same low-power version of the G4 that drives the new PowerBook G4. The 667MHz and 733MHz models use the PowerPC 7450, a new chip that Motorola announced on Tuesday as Apple was unveiling its updated systems. The original G4 systems used Motorola's PowerPC 7400, which had been running at a top speed of 500MHz for more than a year.


The 466MHz and 533MHz G4 chips feature a 1MB L2 cache running at half the speed of the processor. The 7450 in the 667MHz and 733MHz systems has 256KB of on-die L2 cache running at the same speed as the processor. Additionally, the 7450 supports a large L3 cache, with a 64-bit datapath between the cache and the processor. The 667MHz and the 733MHz versions use a 1MB L3 cache located a short distance from the processor.

The 7450 is not just a speed revision. In addition to an on-die L2 cache and a L3 cache, the 7450 uses Motorola's MPX system bus to boost memory bandwidth to more than 1Gbit per second. It also has an enhanced version of the AltiVec vector-execution unit--which Apple calls "Velocity Engine"--that can dispatch two instructions to any of the four vector execution units on the processor.

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The CPU itself still resides on a daughtercard that connects to the motherboard using the same "sawtooth" connector in the previous Power Mac G4 generation. Apple ROMs still reside on the motherboard, so upgrades for this model remain a relatively easy process (photo).

Above the daughtercard is a large heat sink covered by a wide plastic cover. At the back of the heat sink is an exhaust fan that draws air under the plastic cover, along the the heat sink, and out the back of the machine.

The motherboard also features what Apple product manager Jesse Stein described as a "killer memory controller." It now controls the memory, FireWire, the PCI system--including the 4X AGP controller--and the Gigabit Ethernet. Stein characterized it as the Mac's high-bandwidth I/O chip. A separate chip handles USB connections.

The new memory controller supports PC133 RAM. Faster than PC100 RAM, PC133 has slowly become the PC industry standard over the past year. The motherboard has three DIMM slots, each of which can accept up to a 512MB DIMM. So far, Apple has not commented on which variety of PC133 RAM is required, but it appears that the systems ship with CAS-3 RAM.

Faster PCI

Apple has embraced 4X AGP--the previous systems used 2X AGP to drive the video display--and added a fourth PCI slot (photo). The PCI system has been updated to support 33MHz, 64-bit transfer speeds and a feature called "write combining," where write commands are collected and sent over the PCI bus in one burst. Stein said that Apple has tested the PCI system running at a sustained rate of 215MB per second and in bursts of 260MB per second. That's compared with a sustained rate of 100MB per second in Apple's previous systems.

The 133MHz system bus is probably the biggest boon to Mac graphics, said Chris Bentley, project team lead for Mac 3D drivers at ATI Technologies, adding that no software vendor needs to do any work to take advantage of it. The write combining feature, he said, is particularly useful for QuickTime. However, he said the 4X AGP slot is really a future benefit, because no applications are currently facing bottlenecks on the slower AGP bus.

Apple now gives its customers unprecedented choice in the graphics card arena. As BTO options, customers can select from ATI's Rage 128 or Radeon, or Nvidia's GeForce 2 MX. The Radeon is a no-cost BTO option in the 533MHz, 667MHz and 733MHz G4s, but the GeForce 2 MX is the default controller. All of the available video cards support VGA and Apple's ADC (Apple Display Connector).


The 466MHz G4 ships with a 30GB 5400-rpm Ultra ATA/66 hard drive. The 533MHz version ships with a 40GB 7200-rpm Ultra ATA/66 hard drive, and the 667MHz and 733MHz G4 systems each ship with a 60GB 7200-rpm Ultra ATA/66 hard drive. These standard configurations can be changed, and any drive can be selected as a BTO option at the Apple Store. Also, Apple continues to offer a wide selection of SCSI drives and RAIDs for the Power Mac G4 from the Apple store.

The 466MHz, 533MHz and 667MHz Power Mac G4s include a CD-RW drive with a 32X read, 8X write and 4X re-write mechanism. The 733MHz G4 ships with the "SuperDrive," a combination DVD-R/CD-RW made by Pioneer. Stein said the drive is available in limited quantities, so it is presently not a BTO option for the other configurations. "We'll revisit that in the future," he said. The DVD-R/CD-RW mechanism reads DVD at 6X, writes DVD-R at 2X, reads CDs at 24X, writes CD-R at 8X, and rewrites CD-RW at 4X speeds. Apple continues to offer a Zip drive as a BTO option.


Apple has added a proprietary 16-bit connector, the Apple speaker minijack, for use with Apple new Pro Speakers. Otherwise, the speakers are the same Harman-Kardon speakers that ship with the Cube, which use the USB interface. The sound system on the motherboard itself now has a 20W digital amplifier, driving the headphone output and the output for the new minijack. The headphone output is a standard 16-bit analog jack that can support other third-party speakers.

However, Apple has removed the analog microphone jack. An Apple spokesperson said that the Power Mac G4 supports audio input from the new USB microphones, and that most users were using those instead of older analog mics.

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