This Editorial Posted:
March 12th


The PowerPC Problem: A Technical Analysis Of The Mac Processor Techology, Part I

By Tuan Truong
To convert customers from a dominant platform to a smaller niche platform, a common adage is that the niche platform must be 2 to 5 times more powerful, cheaper, or more productive. "Twice the performance for half the [production] cost" of a comparable Intel Pentium was the rallying cry and the expectation of the PowerPC microprocessor partners: Apple, IBM and Motorola, during the heady days of it birth. Apple moved it's primary business to it based on that expectation.

That expectation did not come to fruition, and it seems as if that will still be the case in the future. As of now, the performance of the PowerPC and the Intel Pentium family of processors are in a virtual dead heat in performance and price. There are advantages and disadvantages for each platform, but none approaching the goal of being "twice the performance for half the cost". The following is a set of performance numbers I have gathered for the current PPC 750, the upcoming G4 PPC, and the Pentium II/III on their respective web sites. I'm using base numbers, not peak, as much as I can:

Microprocessor SPECint95 SPECfp95 Process Technology
Moto 400 MHz PPC 750 17.7 11.7 HiP 5 0.25 micron
Moto 400 MHz PPC G4 18 18 HiP 6 0.22 micron w/Cu
IBM 400 MHz PPC 750 18.0 12.7 IBM CMOS7S w/Cu 0.20 micron
IBM 466 MHz PPC 750 20.5 12.3 IBM CMOS7S w/Cu 0.20 micron
Intel 500 MHz PIII 20.6 14.7 Intel 0.25 micron

By the end of 1999 Intel and Motorola are expected to have moved the PowerPC G4 and Pentium III class of processors to a 0.18 micron process enabling them to clock their processors in the 600 MHz to 800 MHz range. IBM will probably stay with their brand new CMOS7S 0.20 micron process with copper interconnects in the near future, but they have yet to include their Silicon-on-Insulator technology which should enable them to clock their PPC processors in the 600 MHz to 800 MHz range as well.

Performance-wise, the SPEC benchmarks does not bode well for PPC G4 systems. The capabilities of Motorola's AltiVec and Intel's SSE (KNI) are a bit of a wildcard due to application support, and benchmarks are going to prove tricky to interpret. Overall, AltiVec should be better per clock rate considering its better design and Motorola's focus in media processor and DSP markets. The floating point in the G4 is a healthy improvement to the PPC 750/604e and is clearly faster than the Pentium III. But the lack of improvement in integer performance is disappointing and indicates to me that the Motorola G4 is just an evolutionary enhancement to the PPC 750 plus the addition of AltiVec unit. Overall, the preliminary performance numbers do not come close to the "2 to 5 times better" goal for moving people off a dominant platform to a much smaller competing one. I expect the Pentium III to be comparable to the Motorola PPC G4 in the personal computer space. The PPC G4 should perform admirably in the embedded markets where the AltiVec will dominate.

What seems worse is the sad state of the memory and I/O architectures supporting the PowerPC microprocessors. Neither IBM nor Motorola seems to produce an AGP/PCI bridge and memory controller chipset. The Yosemite architecture is fine, very good, except for the lack of AGP and being able to address 2 GB of RAM which are limitations in the current Motorola MPC106 "Grackle" PCI bridge/memory controller chipset. I haven't found much on what IBM and Motorola are planning for the PPC memory and IO architecture, only that the G4 will eventually move to a 128 bit system bus, while Intel is driving towards AGP 4x, Rambus, PC133 SDRAM, PCI-X, and NGIO. This may be indicative of Motorola's and IBM's focus on the embedded markets for their PPCs. The market does not need such flexible and high performance technologies. This is where Apple will have the most problems. If you can't feed the processor, you won't get the maximum performance out of the processor.

Just like back in the late 80s and early 90s where Motorola dropped the ball in improving the 68k architecture, Motorola and IBM are both dropping the ball with PPC development. By concentrating on the embedded market rather than the personal computer market they are failing to improve it at a faster rate than the x86 line. If Apple's plans are to compete and gain market share against the "Wintel" and Linux/x86 world, this lack of PPC and PPC subsystem development becomes a major pitfall in that plan. The PPC platform will have parity, but it will not have the generational leap in performance nor price advantage to make it easy to gain market share. With Mac OS 10 (Consumer), Apple has a very portable operating system given that Carbon was designed and implemented right. I think it would be time for Apple to consider moving away from PPC, Motorola at least, and look at another architecture or another strategy.

Next week Tuan offers a possible alternative that may address the needs of the Mac platform in Part II of "The PowerPC Problem: A Detailed Analysis Of The Mac Processor Techology."