Future of the PowerPC

A decade ago, Apple, IBM, and Motorola decided to team up and create a RISC processor that all three companies would be able to use in their products - and sell to others.

For Apple, this meant the opportunity to help shape a processor family that would work well with the Mac OS and allow Apple to abandon Motorola's 680x0 family of processors for theoretically superior RISC processors. It also meant two sources for CPUs, IBM and Motorola.

For IBM, this meant that the processor used in their RS/6000 workstation would form the basis of the new architecture. (The RS/6000 ran AIX, IBM's implementation of Unix. IBM also has a similar POWER architecture that shares many features with PowerPC. See PowerPC from FOLDOC for more details.)

For Motorola, it meant abandoning its 88000 RISC processor and folding some of its technology into the PowerPC program. It also meant Motorola would have to share sales of CPUs with IBM, and also pointed to the end of the 680x0 family of CPUs in personal computers.

History of the PowerPC

Apple shipped the first Power Macs, models based on the PowerPC 601 processor, in March 1994. This processor ran at speeds from 60 MHz to 80 MHz intially and eventually reached the 120 MHz mark.

The PowerPC roadmap split in two different directions from here. The 603 would be for consumer and low power consumption applications, while the 604 would be a more powerful chip designed for workstations and servers.

The 603 debuted at 75 MHz in the Performa 5200 and 6200 in April-May 1995. Besides the design flaws that earned both of these the Road Apple label, Apple discovered that the on-chip cache was too small to work efficiently with the 680x0 emulator. Since the emulator was needed for both old applications and large parts of the OS that had never been recoded for the PowerPC, the 603 was replaced with the 603e, which had a twice-as-large cache. The 603e eventually reached 300 MHz in the Power Mac 6500.

The 604 showed up at 120 MHz in the Power Mac 9500 (May 1995). Apple used the 604 at 120, 132, and 150 MHz in various models, and the chip eventually reached 180 MHz and was used at that speed in the Power Computing Power Center.

The 604 was redesigned with a twice-as-large cache and eventually achieved speeds of 350 MHz in the Power Mac 9600.

In November 1997 Apple released the PowerBook G3 and Power Macintosh G3, both based on the new "consumer" chip, the PowerPC 750. Running at speeds of 233 to 266 MHz, it easily held its own against the 604e at 350 MHz, and the G3 soon became Apple's only CPU.

Nearly two years later, Apple unveiled the Power Mac G4, which was the first Mac with a "pro" processor since the 9600. The G4 was initially promised in speeds of 400 to 500 MHz, although Apple eventually had to scale that back to 350 to 450 MHz due to production problems at Motorola.

Almost three years later Apple is still building computers around the G3 and G4 processors. G3 models run as fast as 700 MHz, and the fastest G4 models use 1 GHz CPUs.

At the same time, Intel is shipping 2.4 GHz Pentium 4 processors.

Multiple Processors

IBM has also been developing the POWER family of processors, which is uses in all its "real" computers. For sheer processing power, IBM already sells models using as many as 32 1.3 GHz Power4 processors. IBM's road map already points to an even more powerful Power5 in 2004 and Power6 in 2006. These models will support up to 64 processors.

IBM is also expected to release a faster, second-generation Power4 later this year.

While multiple CPUs has been an option for some time, they weren't an option for the Mac OS until the DayStar Genesis was introduced as a four-CPU model in October 1995. Apple licensed the technology for their dual processor 8600 and 9600.

Then it disappeared with the G3, since the PowerPC 750 simply was not designed to function effectively in a multiple processor setting. Apple finally reintroduced the "two brains are better than one" concept with the dual-processor Power Mac G4 MP in July 2000. Of course, this wasn't done because Apple thought dual-processors were the best way to go, but because Motorola was still unable to produce G4s faster than 500 MHz.

Why do I say that? Because as soon as Motorola broke the 500 MHz mark in January 2001, Apple introduced models using a 133 MHz bus and running at 466, 533, 667, and 733 MHz - but only the 533 MHz version was offered with two CPUs. Last July's Quicksilver models ran at 733 and 867 MHz, with a dual processor model running a pair of 800 MHz G4s.

It wasn't until this past January that Apple decided that the most powerful Mac should have two CPUs and the fastest MHz rating. I think they've finally figured out that people who want the most power don't want the stigma of not having the highest MHz rating.

Megahertz Hurts

No matter how you slice it, though, thanks to Apple's decision to adopt the G4 as its flagship, Motorola has helped Apple lose the megahertz war. Even a dual 1 GHz machine pales in comparison to 2.4 GHz processors, at least in the mind of marketers and less than savvy consumers. The Megahertz Myth is not going away.

IBM was demonstrating 1.1 GHz G3s years ago and could probably produce a 1.3-1.4 GHz G3 in short order if there were any demand for it. But Apple won't let any Mac run a G3 faster than a G4. In the current Apple universe, the G3 stops at 700 MHz and must never surpass the clock speed of the G4.

Apple and AMD can talk MIPS and GFLOPS until they're blue in the face, but from a marketing standpoint it's MHz and GHz that people understand. Unless the non-Intel world can come up with a meaningful performance spec to clearly measure true CPU power, the Megahertz Myth benefits Intel and hurts all competitors.

In part 2 we'll look at ways to address this and other issues.