Digital Video Questions? Answers from an Expert
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DMN: The disk is the bottleneck. So what kind of disks are you talking about here? Which ones are you using?
Bryant: Right now we're using Ultra 160, we're going to move to Ultra 320, we're using Ultra 160 to EIDE right now, we're going to change those to Ultra 320 to EIDE. We're trying to get cheap, cheap, fast, fast disk arrays out there. If we're on two disk arrays on our nex-gen stuff, we'll probably be running 225 to 230 MB/sec off disk array.
DMN: And you'll need more than that if you want real time uncompressed HD.
Bryant: Yes. If we go a bit bigger than that, like four disks, or four blocks striped across on two different busses, then we're up in the 450MB/sec range -- there we can actually see the rendering drop-off, meaning instead of 1.4 seconds, we're below a second to render a one-second dissolve. That's because we're fast enough to utilize more of the CPUs where they can spawn multi-threads. And that really brings down the rendering time so it becomes more interactive, because of the fact we're using faster disk arrays. They come into play if you aren't able to use the full power of your CPUs because they're waiting for the data from the array -- that's what happens if you can't get the information off disk array fast enough.
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DMN: What about RAM? How much do you need, how is it used and how much is too much?
Bryant: RAM is used by different programs at different times. Like After Effects, if you want to do a RAM preview, more RAM is better because you can actually see more and more of your comp line that you can preview into RAM and play back.
DMN: Is there a limit to the amount of RAM you can use with Windows XP or 2000?
Bryant: If you look at any 32-bit processor, you're limited to 4GB anyway. It's 2 to the 32nd power. So you're stuck at that. There are ways around it, like for Windows 2000 Advanced Server can cheat, giving you the ability to go above 4 gigs, but theoretically, the most RAM a 32-bit processor can map is 4 gigs of memory-- it doesn't understand anything higher than that unless you do some faking of the RAM tables.
DMN: Maybe that's why the latest AMD motherboards top out at 4 gigs of RAM.
Bryant: They're four gigs, but they use a little bit of that 4-gig addressable memory by the AGP port, so it's actually 3.85 gigs, which is not great because you can't actually go to 4 gigs, but that's ok.
DMN: We noticed that problem when we stoked a computer with four gigs of RAM and it showed less than that. That would be the overhead, I guess.
Bryant: It's the overhead of the AGP bus -- it takes up some of that addressable memory that you can't get back unless you deactivate the AGP port.
The good thing is, 64-bit processors are coming out, eighth-generation Athlon, McKinley. With 64-bit, that 4-gig limit then goes to 2 to the 64th power, an ungodly amount of memory, way over a terabyte. You won't be limited to how much memory you can put in it -- most people aren't going to go much higher than eight gigs, sixteen gigs, just because the software architecture can't address it anyway.
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