The Future of Early G4 Power Macs in the Age of Leopard

In November 1997, Apple made the leap to the G3, the first PowerPC CPU optimized for the kind of software computers ran. Less than two years later, Apple abandoned the 300-450 MHz G3 in its Power Mac line by introducing the first Power Mac G4 models.

The G4 CPU had three advantages over the G3: It could access memory more quickly, was designed for multiprocessing environments, and included the AltiVec "velocity engine". AltiVec brought something new to the Mac: SIMD (Single Instruction, Multiple Data), the ability to process multiple pieces of data using a single instruction.

AltiVec can process 128 bits of data at a time: 16 8-bit values, eight 16-bit numbers, or four 32-bit numbers can be processed in parallel, all at the same time. This made AltiVec especially potent for processing images, both still and video. Photoshop and video programs were among the first to take advantage of the new velocity engine.

With Mac OS X 10.5 "Leopard" rumored to require a G4 CPU, these are the oldest Power Macs that could conceivably run it - and with recent claims that Leopard will require an 867 MHz CPU, that may only be possible with a CPU upgrade, if at all.

The First G4 Generation

Announced on August 31, 1999, there were three different models. The entry-level model, code named Yikes!, essentially grafted a G4 CPU on the same Yosemite motherboard used in the Blue & White G3. The new case was graphite gray, and the new model ran at 400 MHz. It had the same 66 MHz 32-bit PCI bus for its ATI Rage 128 plus three 33 MHz 64-bit PCI slots as the G3 model.

This created a new paradigm for entry-level Power Macs that would survive well into the G5 era where the least costly model would in some way be more compromised than the faster ones.

Introduced at the same time was the "Sawtooth" Power Mac G4, which had an entirely new motherboard designed to take advantage of a faster memory access mode supported by the G4 (but not the G3). It was also the first Mac with an AGP video slot; the AGP 2x slot provided a lot more bandwidth than PCI ever could even though it initially used the same ATI Rage 128 chipset found in Yikes! and the Blue & White. Unlike PCI, which is a general purpose bus, AGP was designed specifically for video and can read data from system memory directly.

Apple has used AGP 2x, 4x, and 8x. Maximum throughput is 533, 1066, and 2133 MBps. AGP 1x has the same throughput as 66 MHz 32-bit and 33 MHz 64-bit PCI slots; Apple never used AGP 1x.

The entry-level Power Mac G4 was introduced at 400 MHz with a US$1,599 retail. The more powerful AGP models had DVD-ROM drives (instead of CD-ROM) and were announced at 450 MHz and 500 MHz at $2,499 and $3,499 respectively. You could save a whole lot of greenbacks by choosing the Yikes! model.

Unfortunately Motorola was unable to produce 500 MHz G4 CPUs in sufficient quantity, and on October 13 Apple did the unthinkable: It reduced the clock speed of the new G4 models without any change in price. Needless to say, there was an uproar.

On December 1, Apple discontinued the 350 MHz Yikes! model, replacing it with a 350 MHz AGP Power Mac G4. And Apple finally got the 500 MHz Power Mac G4 out the door on February 16, 2000, discontinuing the 350 MHz model at the same time to keep the simple three-model line.

'Two Brains Are Better than One'

While IBM was moving the PowerPC G3 processor well beyond 500 MHz, Motorola and the G4 were stuck at 500 MHz. Unable to offer more speed, Apple introduced the first dual processor Power Mac G4 models on July 19, 2000. The entry-level model ran at 400 MHz and was virtually identical to the earlier Sawtooth. The only change was support for Gigabit Ethernet.

The 450 MHz and 500 MHz "Mystic" Power Macs had two CPUs, which theoretically doubled its computing power. Theoretically, because the classic Mac OS didn't support multiple processors, although a handful of applications (such as Photoshop) did. It wasn't until Mac OS X shipped that Apple had an operating system designed to take full advantage of two CPUs - and a lot of OS X software followed suit.

Approaching the Age of Leopard

Power Mac buyers always get the newest CPU technology, but that also means that early G3 and G4 Power Macs offer far less CPU speed than later PowerBooks, iMacs, and iBooks. Fortunately all of the Power Macs can accept a CPU upgrade, making it possible to take these to the gigahertz range and beyond.

Unfortunately these are older Macs with some hardware limitations. The system bus runs at 100 MHz, the AGP 2x slot may be incompatible with AGP 4x and later cards, there is "only" room for 1.5 GB of RAM ($145 at today's RAM prices), and the Ultra ATA/66 drive bus is limited to a maximum hard drive size of 128 GB without the use of special drivers.

None of these have been obstacles to running Mac OS X 10.0 through 10.4 on these early G4 Power Macs.

Yikes!

Because of its PCI video bus and because it doesn't use the faster memory access mode the G4 supports, the Yikes! Power Mac G4 is the least likely to run Leopard well, if it can run it at all. Due to its many limitations, we recommend not even attempting to use Leopard (someone is bound to come up with a hack!) except to see how well or poorly it performs.

The 350 MHz and 400 MHz Yikes! models are the dregs of the Power Mac G4 and will undoubtedly be far superior Tiger (Mac OS X 10.4) machines than Leopard ones.

Sawtooth

With AGP graphics and superior memory access, the Sawtooth models and the single-processor Mystic are far better suited to OS X than Yikes! These are the oldest Macs with AGP support, and although the ATI Rage 128 video isn't supported by Quartz Extreme, it is possible to put in an ATI Radeon AGP video card to obtain Quartz Extreme support. (Quartz Extreme does the same kind of thing Core Image does, offloading graphics processing to the video card, but on a much lesser scale. Quartz Extreme requires AGP graphics, ATI Radeon or nVidia GeForce2 MX graphics, and 16 MB of video memory.)

The AGP models also accept a lot more CPU upgrade options than the Blue & White G3 and Yikes! G4 Power Macs.

Mystic Dual Processor

Although of little benefit in the days of the classic Mac OS, dual processors really came into their own with the arrival of OS X. The entire operating system is multiprocessor aware, and many parts of the OS and many applications take advantage of dual-, quad-, and even eight-processor hardware.

While Sawtooths are generally incompatible with dual-processor upgrades, the dual processor Mystic Power Mac are fully ready for them. While the overall benefit of two CPUs varies by task, a computer with two CPUs can perform some tasks twice as fast as the same computer with one CPU at the same speed. At worst, programs that aren't multiprocessor aware won't be any slower, so there is a net gain. On average, we estimate a dual processor computer is as powerful as a single CPU running 60-75% faster, making the 500 MHz Mystic roughly equivalent to an 800-875 MHz single processor G4.

Again, we suspect that these Macs will not be officially supported by Leopard, and we're also pretty sure that someone will find a way to get Leopard running on them. We wouldn't expect world class performance from them, but we think that these could be very competent (albeit a bit slow) Leopard machines.

With the right AGP video card, it's conceivable that you could have full Core Image support, and if you're willing to "flash" the Windows version of the Sapphire Radeon 9600, which you can buy refurbished for $27 on eBay.

Bear in mind that AGP 4x and later video cards may be incompatible with the Sawtooth and Mystic models, as there are voltage differences between the AGP 2x (3.3V) and AGP 4x (1.5V) specifications. Many cards are designed to support both voltages, but check before you buy and again before you install.

Bear in mind that it's not easy to find Mac video cards. One workaround is to flash the ROMs in a Radeon or GeForce card intended for Windows PCs, and The Mac Elite is a great resource for people who want to do that. They also have an article that explains how to get some AGP 8x cards working in older G4 Power Macs with nonstandard AGP sockets.

Closing Thoughts

We're Low End Mac, so we're disappointed that it appears that all G3 Macs and a lot of G4 Macs are not going to be supported by Leopard. We just hate seeing an operating system get so bloated and weighed down with eye candy that it makes older Macs obsolete, but Apple doesn't seem to feel the same way.

Even if it is possible to run Leopard on these early G4 Power Macs, we suspect that Tiger will be the superior operating system on this hardware. For those serious about hacking Leopard for old G4 Power Macs, we recommend dual processors, lots of RAM, a fast hard drive, and an AGP video card that supports Core Image.

It may be more cost effective to buy a newer model, but if you already have one of these and want to give Leopard a try when it's released, we'd love to hear from you.

UPDATE: We have received several reports of Leopard running successfully on Sawtooth and Mystic Power Macs, and our article on Unsupported Leopard Installation has several tips on installing OS X 10.5 on unsupported Macs. However, we have not yet received a report of Leopard running on the Yikes! mode. 

Further Reading

• Low End Mac's best used Power Mac G4 deals, updated biweekly.
• How big a hard drive can I put in my iMac, eMac, or Power Mac?
• Guide to Power Mac G4 Upgrades for Power Mac G4 with AGP Graphics
• Make AGP 8x video cards work in G4 Power Macs, The Mac Elite. Instructions for disabling pins 3 and 11 so Mac compatible AGP 8x video cards will work in most G4 Power Macs.