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Anthony Frausto-Robledo, Editor ([email protected])
30 Jul 00 Second Update: 4 Aug, 8:15am [See comments in red]


AltiVec and multiprocessing in CAD/3D

In this article: The strengths of the G4's architecture.

If you read our exclusive interview of Sean Flaherty, CTO, of Nemetschek N.A., you may have been surprised to hear him say that AltiVec doesn't get VectorWorks that much in terms of speed up. The reality is this comment is somewhat missing leading.

" I think technology that speeds us up WITHOUT requiring a lot of work as the best type of improvement." — Sean Flaherty, CTO, Nemetschek NA.

The PowerPC G4 processor with the AltiVec instruction set is a superior chip architecturally for science and 3D visualization than anything coming out of Intel. Over the next two years, with perhaps particular emphasis on 2001, we'll see a number of amazing feats in 3D visualization running on Power Macs with the G4 processor. To borrow words from Billy boy himself, "the best is yet to come."

Let's Get Down to Facts

Let's talk about Sean's comments for a second. Sean mentioned that "AltiVec primarily speeds up two major types of operations: bit array manipulation and single-precision floating-point." Some of you may be missing the word 'major' in there. That's important. Bit array manipulation is a 'major deal' in rendering and animations (which are frame by frame sequences of raster images), as well as image optimization processing—like the kind done in Photoshop and graphics and video applications geared toward the Web. That's why Adobe says the Power Mac G4 is the ultimate Photoshop machine, and why that little 'G4 AltiVec plug-in' that ships with the latest version of Photoshop is so important to you if you have a G4.

When Sean mentioned that AltiVec doesn't gain VectorWorks that much in terms of speed up he was primarily speaking about 2D/3D CAD processing, not OpenGL or QD3D-based full color rendering with texture mapping. Although an important part of any CAD program, rendering in VectorWorks is just one of many larger segments of the program. Still, I was a bit confused and asked him to clarify some issues:

AFR: Sean, this makes AltiVec should like it misses the boat on helping CAD applications and will likely confuse readers about all of Apple's hoopla about Velocity Engine [Apple's term for AltiVec] and rendering 3D rendering apps. Did Apple make a mistake with AltiVec here?

SF: I don't think Apple missed the boat at all. They sped up many raster techniques such as texture mapping and image composition, the things that make interactive display of 3D objects work very quickly. We support AltiVec by using OpenGL. For some reason, people see this as us not supporting AltiVec or AltiVec not supporting our needs, but I see it as a new chip architecture that speeds one of the slowest operations in VectorWorks. I think technology that speeds us up WITHOUT requiring a lot of work as the best type of improvement.

Sean mentioned that AltiVec provides a tremendous speed up in VectorWork's rendering, especially with texture mapping, a very important part of high-end rendering and animation. He also said that many may confuse a chip that accelerates floating-point with accelerating all scientific apps across the board. That just isn't true, as these programs use different programming techniques.

The G4: weaknesses and strengths

The G4 with AltiVec is not perfect. One current draw back, which Motorola is reportedly working on, is the single precision floating-point processing. Double-precision is what the G4 should provide and will help tremendously with luring back high-precision CAD/CAD/CAID programs to OS X. [This paraphraph needs clarification. The G4 chip does support double-precision floating point. Only AltiVec is limited to single precision vectors.] {see other comments below}

Another weak area currently (and will supposedly be remedied this Fall) is the processor cycle speeds on the G4. The G4 is losing the megahertz war to the Pentium III's and AMD Athlons. It's amazing how quickly this can change. It was not too long ago that the G3 was ahead and equal in terms of megahertz alone. Currently the G3 in the mobile market is not that far behind Intel in terms of mehahertz alone.

Thankfully, megahertz isn't the only and major factor affecting chip performance. If that was the case Pixar, Disney and Lucas' ILM wouldn't be making movies like Star Wars and Bug's Life on processors currently running at half the speed of Intel's Pentium III. But they are. Those RISC-based MIPS and other UNIX processors providing the firepower behind their high-end workstations, ganged together in render-farms of hundreds of machines, not only run at speeds approximate to the G4's current limit, they, like the G4, are true RISC (reduced instruction set computing) microprocessors.

One of the most overlooked advantages of the G4 processor is its RISC architecture. "In the industry", according to previously published quote by Sean Flaherty, "the G3/G4 chip architecture is known for its incredible math performance, both integer and floating-point." It is not surprising then to learn about the parallel supercomputing G4 clustering projects at leading universities like UCLA. And it should not surprise you to learn that more scientific and advanced 3D visualization applications are coming back to the Mac platform, and in full force.

Multiprocessing with the G4

With Apple's introduction of the multiprocessor G4 Power Macs at Expo, we should continue to see advances in the technical market for G4-enabled applications ready to take advantage of both AltiVec and multiple processors. At Macworld Expo, Black Lab Linux demonstrated parallel computing systems with eight (8) G4 Power Macs running AltiVec-enabled Linux apps in excess of 10 times faster (1,000%). The PowerPC architecture not only offers scalable, parallel multiprocessing but offers the highest performance-lowest power consumption per watt of any comparable Pentium system.

When will all of this parallel, multiprocessing power come to our finger tips?

At SIGGRAPH last week Newtek was featuring 13 Power Mac G4s in a render farm running an advanced beta of LightWave 6 for Mac OS X. This was an impressive sign of things to come. Also, Maya for OS X is well advanced at this point and promises to deliver Mac OS X only features in a powerful, multiprocessor ready package.

Over the next year expect to see more high-end 3D visualization and CAD applications come to OS X, complete with both AltiVec and multiprocessing in mind.

[Reader Comments]

According to Larry Rosenstein, who helped point out the correction above, "it's unlikely that we'll see AltiVec operating on double precision vectors anytime soon. That would probably require Motorola extending the AltiVec register size of 256 bits, which would be a significant change."

Larry also mentioned that AltiVec should be useful for matrix multiplication, something that can help 3D applications as well.

Edwin van Spronsen, of Amsterdam, wrote in about emphasizing the difference between the rendering of RT (real time) previews in 3D applications compared to print-ready, high resolution rendering (which takes many hours, or even days, to complete). Edwin mentioned that the latter type of rendering done by every 3D app uses 64-bit floating-point processing (something the G4 itself does quite well without AltiVec). In his opinion, the future support of 64-bit AltiVec was doubtful. Rather, Edwin feels Motorola will concentrate on the the G5.

Should Motorola work hard with Apple to support 64-bit AltiVec? Does it matter more then clock speed? What do you think? When the G4 first came out, test run here at Architosh showed that the floating-point performance of the chip was second to no Pentium chip. However, things have changed quite a bit on the Intel side (and all in just 11 months), first with the push to 700 MHz, then with the climb to 1 GHz, and with enhanced architectures. Now Intel has introduced 1.13 GHz (or is it 1.12 GHz?) Pentium III's.

While the thesis of this article is the G4s superior architecture, we can't deny that the G4 chip has made little progress in the last year—while Intel has made great progress, at least in terms of MHz. Someone needs to seriously kick Motorola's you-know-what into gear. Before this year is over Apple needs to ship G4's running at at least 700 MHz. If it can't, Apple is going to be perceived as making a mistake with choosing Motorola over IBM's PPC roadmap. While AltiVec holds great promise, so too does MHz speed, something we have not seen change with the G4 in too many months.]


Related Articles

Feature: Interview with Sean Flaherty, CTO, Nemetschek NA.

LightWave Featured on Apple G4 Render Farm

Maya for Mac OS X: No Illusion

Apple Debuts New Power Mac G4s with Dual Processors


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