Mac Musings

Will the PowerPC 750vx Appear in Future Macs?

Daniel Knight - 2005.03.10

After publishing Will the Dual-Core G4 Appear in Future Macs? and Will the Cell Processor Appear in Future Macs?, I received several emails inquiring about a rumored G3-plus-AltiVec processor that IBM seems to have been working on for several years.

The PowerPC 750vx, code name Mojave, has been a few months from release for two or three years, according to various rumor sites - and nobody seems to have published anything new about the CPU in over a year.

Back Story

Motorola's problems with G4 chip speed have been the stuff of legends ever since Apple was unable to ship the 500 MHz Power Mac G4 announced in August 1999. It was nearly six months later that Apple shipped the first 500 MHz G4s.

Unable to get faster CPUs, Apple moved to the "two brains are better than one" dual-processor "Mystic" (a.k.a. Gigabit Ethernet) Power Mac G4 in July 2000. And it wasn't until January 2001 that Apple shipped the first G4s to pass the 500 MHz mark. The "Digital Audio" Power Mac ran as fast as 733 MHz.

With Quicksilver (July 2001), Apple hit 867 MHz, and the January 2002 Quicksilver 2 models were the first to reach 1 GHz. G4 Macs reached 1.25 GHz in August 2002, and the fastest Power Mac G4 - running at 1.42 GHz - was released in January 2003.

Since then, Motorola has kept improving the G4, but the fastest G4 Macs, the 2005 PowerBooks, top out at 1.67 GHz. Compare this with 2.5 GHz for the G5 and speeds in the 3.6 GHz range for Intel's Pentium 4.

IBM vs. Motorola

While Motorola was working hard to make the G4 run faster, IBM was moving ahead with the G3, eventually achieving speeds as high as 900 MHz. However, Apple was committed to the AltiVec (a.k.a. VMX) instruction set, which the G4 supported but the G3 didn't.

IBM was of the mind that the greatest improvement came with faster chips; Motorola believed that the future was more powerful ones. Ideally you'd get both, but Apple had cast its lot with Motorola and quickly lost the Megahertz War to Intel.

It took some time for IBM to realize that Apple was the biggest PowerPC computer maker and agree to adopt the AltiVec technology in their next generation CPUs. The G5 was one of those chips, and it powers today's iMacs and Power Macs.

The other, which hasn't yet seen the light of day, is the long-rumored 750vx, essentially a G3 CPU with AltiVec added.

750vx vs. G4

The G4 design has been moving forward, but today it's still on the trailing edge of CPU speed compared with Intel and AMD offerings. Motorola is plugging away at the dual-core G4 (see Will the Dual-Core G4 Appear in Future Macs?), IBM is pushing for more speed on the G5, and the Cell chip appears set to trump everything in 2006.

I don't doubt the claims that IBM was developing a G3-plus-AltiVec CPU that Apple could have used in iBooks, iMacs, eMacs, and the like. From a programming perspective, the only difference between the G3 and the G4 is AltiVec. (From a hardware perspective, the G3 has horrible multiprocessor support.)

Speeds for the rumored chip are in the 1.5 GHz to 1.8 GHz range, with 2 GHz just around the corner. It's probably designed with a 512 KB or 1 MB cache, and it runs on a 400 MHz DDR bus, which offers 2.5-3 times the performance of the 133 MHz and 167 MHz buses used in today's G4 computers.

The 750vx Future

There are also rumors that this project has been killed, in which case this is nothing more than idle speculation. But if the 750vx were real, could we expect Apple to use it?

Good question. It seems that the 750vx and 8641 would be comparable chips. Either would make a good replacement for the G4 currently used in iBooks, eMacs, and Mac minis.

The big difference is that the 8641 will be available in single- and dual-core versions - and both will use the same socket. That means Apple could design a single motherboard and configure it with either a single-core G4 or a dual-core one.

Assuming there's not a huge price difference - and that the 750vx actually exists - logic, marketing, and economics dictate going with the Freescale 8641 rather than the IBM 750vx. One design yields twice as many models depending on which CPU is installed.

The only reason I can conceive for Apple to build a 750vx-based computer would be speed. If the 750vx runs at 2 GHz or faster and the 8641 can't get within 20% of that speed, then maybe it would make sense for Apple to use it. Maybe.

Rumor or not, I don't see the PowerPC 750vx in Apple's future based on what little speculation (and lack of hard facts) I can find on the Internet.

The Mac CPU Future

My guess is that the 750vx project helped pave the way for the PowerPC 970 (a.k.a. G5) that powers today's iMacs and Power Macs. IBM is rumored to be developing a 970gx version of the CPU that will run at up to 3 GHz and have a 1 MB cache.

IBM is also working on a dual-core G5, the 970mp. Both the 970gx and 970mp are part of IBM's Antares project, and it appears that the 970gx is a single-core version of the 970mp.

If the two processors are pin-compatible, it's quite possible that we'll see Apple move the Mac forward with Freescale 8641 (single- and dual-core) in consumer models and IBM 970gx/mp in pro models sometime this year - and possibly adopting the Cell when it's available in 2006.

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