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CB: It depends. Memory speed determines how fast you can 'read from' and 'write to' texture, depth or color buffers in memory. Engine speed determines how quickly you can execute the vertex and pixel shader instructions to calculate pixel positions and colors. Our Radeon X1900 GT/XT cards have a state-of-the-art processing engine. The ASIC is identical on both the PC and Mac versions of the card.

AFR: You know I was recently on a leading CAD company's discussion boards and there was talk about running their Windows-only CAD program on a Mac using Boot Camp or Parallels. Anyway, the discussion devolved into a Mac versus PC hardware comparison and people are really confused about what Macs are physically-- hardware wise--now that they have Intel chips. Some people think that they are just an Apple logo on a PC box with beautiful industrial design. That's just not so.

So what is actually different about your graphics cards for PCs versus Macs, especially now that Apple is based on an Intel Architecture?

CB: Great question. For a long time graphics cards for Apple computers have had to be hardware specific in part because Apple used different connectors. This meant we had to have a physically different main board to accommodate these different connectors.

AFR: So what is specific today on the hardware side for the cards in the Mac Pros? They have industry standard connectors now.

CB: Not a lot on the hardware side. But EFI is a big difference on the
ROM side. Apple's early adoption of this Intel standard has also caused hardware vendors to create special boards just for that.

AFR: So there's not much unique on the hardware side today? EFI is also an Intel standard, should that mean that when Microsoft adopts EFI with Windows Vista and post-Vista, there will be even less of a difference remaining on hardware uniqueness?

CB: It is not clear when or if other PC vendors will adopt EFI, which I
think stands for "extensible firmware infrastructure". Virtually all
other PC graphics cards require a video BIOS, a different kind of
firmware than EFI and different again from OpenFirmware, the type
required by the Power Mac G5 and other PowerPC based Macs. This
distinction between the firmware, the control code typically programmed into a ROM on what otherwise might be identical hardware, determines the system compatibility and operating characteristics of each individual graphics card. It makes them unique from one another and unfortunately prevents the individual cards from being interoperable between one type of system and another--for example from a Power Mac G5 to a Mac Pro or from a Mac Pro to a typical Windows based PC.

AFR: Now what about the software side?

CB: On the software side there is a really interesting story. Apple's OS architecture has very different requirements. Apple's OS X has been doing Vista-like features since version 10.1. Mac OS X virtualizes VRAM. Windows XP does not. This has given Mac applications unique advantages. I remember talking with the Starry Night developers at WWDC 2005. They were rendering the Earth with over 2 GB of texture data, on an ATI graphics card that had only 256 MB VRAM. They could do this because the OS managed paging the texture data on and off the graphics card as needed in the kernel without them having to worry about it. Up until Vista, Microsoft Windows couldn't do that.

AFR: What does this mean in the bigger picture?

CB: Well, Apple's been doing this since 2000. Apple realized early on
that they couldn't do Mac OS X with industry standard PC drivers because those drivers were not written to support the advanced features of Mac OS X's graphics engine. Even though Quartz Extreme was not present in the first releases of OS X, Apple was laying the groundwork for it.

AFR: So Mac OS X is based on OpenGL and advances in hardware accelerated OpenGL have given the Mac unique graphics capabilities. What is happening specifically with Quartz and Quartz Extreme in Mac OS X? And what does this mean in the bigger picture?

CB: In Mac OS X under Quartz Extreme the CPU constructs the picture in apps like Excel or Safari and renders it in software to host memory (RAM), but that picture is then treated as a 'texture' and drawn to the screen using the hardware accelerator (GPU). Now in a usage model like Quartz 2D Extreme, Apple is moving every single piece of rendering to the GPU. Now you are using the graphics hardware to draw every single dot, every character, every line.

AFR: And how much faster is that?

CB: It can be 2-200 times faster, depending on the operations. In
average usage situations it might result in a more reasonable 3-4x
boost. [For an excellent Ars article go here.]


Apple and OpenGL Development

AFR: Earlier we were talking about OpenGL and how Apple depends on it for its advanced user interface in OS X. Where is your work going with OpenGL and Apple?

CB: ATI's work has historically been in three realms for Apple. These
started with games, pro apps like CAD and 3D, and then the OS itself in OS X. Now there is a fourth realm.

AFR: Which is...

CB: Apple's own Pro apps!

AFR: What are the differences?

CB: Well, games are full-screen OpenGL based programs that hog all the available resources. They are very concerned with efficiency, and their design cycle is short enough that they tend to heavily use the latest OpenGL fast paths. At the other end of the spectrum, Pro apps may use a broad range of OpenGL functionality, but they are typically not rewritten very frequently, so they usually do not rely on the latest OpenGL fast paths. Many Pro apps only use hardware accelerated OpenGL for preview mode, so there is less incentive for them to be on the bleeding edge of OpenGL features. So, games and traditional Pro apps drive OpenGL in different ways.

With Quartz Extreme Apple added the OS Window Server as an OpenGL client, treating each window as a texture. Quartz Extreme put pressure on the OpenGL drivers to optimize code paths that games and Pro apps had never cared about, and flushed out a whole class of bugs that games and Pro apps had never encountered. Each of these steps led to the further evolution of the [GPU] drivers.

In some ways, the use of OpenGL by Apple's own Pro apps, like Motion, Shake, Aperture, Final Cut Pro and also Pages, Keynote, FrontRow, Quartz Composer, PhotoBooth, etc have forced the biggest evolutionary leap in the drivers. Apple's Pro apps stand apart because those things are pushing the envelope of OpenGL features. They are pushing the envelope and they are also a window into OpenGL's future.

AFR: Sounds interesting. Keep going.


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