PowerPC 970

Introduction

Even before their June 23rd announcement by Apple (following a widely reported leak the previous week!), it was well known that the next generation of Power Macintosh computers would be based on the PowerPC 970 chip. This IBM-developed chip, which Apple calls the G5, is much more powerful than the chips referred to as G3 and G4. In this article, we'll look at the new chip, its features and performance.

What IBM Said

In early March 2003, a press release from IBM suggested that the Power PC 970 would be clocked up to 2.5 GHz. Mac rumor sites immediately announced that the 2.5 GHz chip was already running in the lab and that Macs based on this part would soon be blowing away Intel's fastest chips. Although the real story turned out a little differently, Apple can still claim "the world's fastest personal computer."

On Mar. 11, 2003, IBM announced that initial shipments of the PPC970, the first in a new family of high-performance 64-bit PowerPC microprocessors, would be delivered at clock speeds up to 1.8 GHz, with volume production slated to begin in July 2003. This seemed consistent with earlier statements and technical information posted on IBM's Microprocessor Forum website in Nov. 2002.

Fortunately, the company was somehow able to push the clock rate up to 2.0 GHz for the dual-CPU model touted by Apple as "the world's fastest personal computer." IBM now says that  2.3 to 2.5 GHz chips will be the generation after the next. In other words, they're not coming anytime soon.

What Apple Says

Apple, of course, says its G5-based Macs are the world's fastest personal computers, and Apple VP Phil Schiller demonstrated the G5's prowess in 3-D rendering, Photoshop imaging and mathematical number-crunching to prove this point, at the product's introduction on June 23rd.

At his announcement of  Apple's G5 Macs, Steve Jobs said the new machines were slated for delivery in August. One day later, the online Apple Store listed the earliest available delivery date as Sept. (There's usually at least a few months' gap between the onset of production and the release of commercial products.)

Apple has a developer note highlighting the differences between the G4 and the G5. The "DOs and DON'Ts" section, which highlights some incompatibilities between the two chips, is particularly interesting.

It is also known that the PPC 970's initial production run is based on a .13 micrometer fabrication process and Copper/SOI CMOS technology. Even the 2.5 GHz version of the chip, when it appears, is expected to be based on this .13m fab. The company has also confirmed that the 64-bit CPU has an on-chip 512 KB L2 cache, AltiVec Vector/SIMD unit, and 6.4GB/s I/O system bus throughput. According to Apple, the FSB runs at speeds of up to 1 GHz. More precisely, it runs at one half the CPU speed. In other words, the 1.6 GHz model's FSB is 800 MHz; the 1.8 GHz model's FSB is 900 and the 2GHz Mac's FSB runs at 1GHz.

At this writing, it's unclear how many PPC970 processors IBM can deliver to Apple -- after all, the chip, at the time of the Apple introduction, wasn't even in "volume production" -- that isn't slated to happen until July 2003. Thus, it's unlikely that "mass market" Macs based on the part will be made available anytime soon, and even less likely that Apple will announce faster models before Q1/04. The real risk is that the PPC970, if the entire Mac line does not migrate to it quickly, might dampen sales of all G4-based models. It's also interesting to note that Steve Jobs felt compelled to discuss an unavailable 3 GHz version of the CPU. Conventional wisdom holds that companies should never pre-announce products they can't deliver, as this can impact current sales. (Steve Jobs is old enough to have learned that lesson from Adam Osborne.) However, in this case, Jobs' comment was probably justified: Mac users, jittery after years of near-stagnation from Motorola, need to feel that Apple and its G5 chip partner IBM have a roadmap for future chip development. With a single statement, Jobs unequivocally confirmed this.

What the Experts Say

A May 5, 2003 commentary by Hannibal of Ars Technica on Slashdot suggests that the PowerPC 970 may not be as well-rounded as its most ardent proponents hope. He characterizes the 970’s group dispatching scheme as "bad" and says the way it dictates how one ALU is fed from dispatch slots 0 and 3, while the other is fed from dispatch slots 1 and 2 is a performance killer.

He continues, "Now, this is potentially bad enough already. But when you factor in the fact that the ALUs are not symmetrical, and that certain types of ops can only go to one ALU and hence MUST go into one of only two dispatch slots, then you get a recipe for further choking of dispatch bandwidth."

The end result, he says, "is that the 970’s ALU hardware is weaker than that of the G4e, the P4, and the Athlon. So its clock-for-clock integer performance will be worse, at least this is what I’m predicting. We’ll see if I’m right."

The Media Chime in....

Interestingly, however, it appears that Apple may be fudging some of the numbers a bit to make its point. There is a significant discrepancy between the performance Apple claims its competitors offer, and the claims of Intel and Dell. Indeed, there is evidence to suggest that the  2 GHz dual-CPU Power Mac G5 is in fact slower than a  3.06 GHz single-processor Dell PC. And that's not even Dell's fastest Pentium 4: it also offers a 3.2 GHz model.

Even more damning are the Oct. 2003 tests conducted by PC World, which found that Apple Power Macs did well on Photoshop, but the 64-bit AMD-based systems won handily on most tests -- and ran at least twice as fast in several instances.

Elsewhere, critics charge that Apple's SPECmark test results don't gibe with the official SPEC results obtained by other companies.

Some are accusing Apple of deliberately using the non-optimized GCC compiler on the Intel platform to make its competition look bad in this comparison.

The Register casts a skeptical eye at Apple's numbers:

• On one hand we have figures that suggest the 2GHz G5 outperforms the 3GHz Xeon in certain benchtests, and on the other we have numbers that show the exact opposite. What gives?
• Firstly, Dell's own figures were calculated using different compilers and host operating system: Windows XP Pro, Intel's own C++ and Fortran compilers, and the MicroQuill SmartHeap Library 6.01. Secondly, the compiler used by VeriTest, GCC, is said to generate code that less well optimised for x86. Thirdly, VeriTest seems to have adjusted the test hardware to favour the G5. Again, all the details are there in the documentation.
• VeriTest admits it used an Apple-supplied tool to adjust the G5 processor's registers "to enable Memory Read Bypass" and "to enable the maximum of eight hardware prefetch streams and disable software-based pre-fetching". The company also installed a "high performance, single-threaded malloc library... geared for speed rather than memory efficiency". That, says VeriTest, "makes it unsuitable for many uses".
• We'd guess these are hardly standard system configurations. 
• VeriTest also says it tweaked the Dell boxes. For example, when it came to the SPECint and SPECfp rate tests, it disabled HyperThreading, though enabled it for the base SPECint and SPECfp tests. While the compilers were set to optimise code for the Pentium 4, SSE 2 instructions were not used to speed floating point maths operations, only SSE 1 instructions were enabled. VeriTest provides no clear rationale for these choices.

There are also people accusing Apple of ignoring the Athlon MP in its comparisons, knowing full well that the AMD chip would have turned the tables in virtually all of the integer math tests. And it has already been shown that the AMD Opteron, using Intel's compiler, manages to beat the 970 in both SPECint and SPECfp tests. One thing's for sure, though: the new Macs are more than twice as fast as the company's previous high-end G4s in many tasks. And, for many professional Mac users, this is all that really matters.There are many ways to compare G4 vs. G5 performance. One is the Skidmarks GT benchmarking utility that's part of Apple's CHUD performance tools. Think Secret ran a test providing a rough comparison of G5 and G4 performance. The Skidmarks scale, reports TS, has "100" equal a Power Mac G4 at 1GHz. The Dual 2GHz received scores of 172 for integer performance, 270 for floating point performance, and 208 for vector performance.

In another widely publicized benchmark test, NASA compared a 2 GHz G5 against a 2.66 GHz Pentium 4 in computational fluid dynamics simulation tests. In these tests, which rely heavily upon floating point calculations, the P4 beat any single-CPU G5.

And, in our own tests, a Pentium 4 running at a mere 1.4 GHz beat Apple's 1.6GHz and 1.8 GHz single-CPU G5 configurations in multitrack audio playback and effects processing.

However, as noted in our G5 report elsewhere in this section, these findings don't change the fact that the G5 is by far the fastest computer Apple has ever shipped. And for most Mac users, that's all that matters.

Power Draw

The 1.8 GHz PPC 970, according to IBM, draws approximately 42-48W of power. The 2.5 GHz part based on a .13 micron fabrication process, says IBM, will draw 64W. For comparison, a 3.06 GHz Pentium 4 -- a notoriously power-hungry chip -- draws 81.8W. Things start looking even better for the PPC970 at lower clock speeds. A 1.2 GHz PPC970 is expected to draw only 19W. This bodes well for the prospect of PPC970-based PowerBooks -- probably clocked at lower rates than the desktop models. (PCs, of course, can use lower-power mobile chips such as the Pentium M. IBM already boasts a battery life of up to seven hours for its 5-pound ThinkPad T40 1.7GHz notebook based on the new chip.)