What are Fast Writes?

Discussion in 'Architecture and Products' started by Smurfie, Aug 4, 2004.

  1. Smurfie

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    Is there any good explanations or writeups on this "feature"? What are its uses or functionalities? What benefits does it bring?

    ps. I did a search already, but didn't find anything complete or comprehensive, but rather, a huge collection of smatterings. It would be good if someone could really explain it in detail, so that enthusiasts will be more informed to what this checkbox does.
     
  2. digitalwanderer

    digitalwanderer Dangerously Mirthful
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    A pain in the ass and a system locker-upper.

    Only leave it on if you have to, and you only have to for certain AIW and 9600 cards.

    Disable it, you're MUCH better off!
     
  3. KimB

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    Typically the full AGP bandwidth is only usable from system memory. That is, the card will read data straight from system memory at full speed.

    Fast writes are a way for the CPU to get in on that high bandwidth without having to first write to system memory. So, fast writes are, in essence, a way to save system memory bandwidth for many tasks.

    Now, they don't always work as intended, and with some hardware and/or drivers, they actually will slow a system down. So, fast writes are one of the first things to turn off if you have any stability problems, for example.
     
  4. Smurfie

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    Is it in anyway related to DMA?
     
  5. MasterBaiter

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    Sounds a helluvalot like it doesn't it? :?
     
  6. KimB

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    DMA is direct memory access: a way for devices to pull data directly from memory. Yes, normal AGP operation (without fast writes) is exactly like DMA. Fast writes is a way around DMA, to allow the CPU to send data directly.
     
  7. Smurfie

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    So Fast Writes is a way for the CPU to write directly to the graphics card across the AGP bus, whereas disabling it, requires the CPU to write to system memory first, before it is sent to the graphics card?

    Correct me if this is wrong. Thanks!
     
  8. Neeyik

    Neeyik Homo ergaster
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    That's pretty much it.
     
  9. KimB

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    The only thing is, with 3D graphics, data is typically cached in system RAM, so you wouldn't want to write directly from the CPU anyway.
     
  10. Nick Spolec

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    MAME emulation benefits from Fast Writes, actually.. Because MAME does a lot of writing from the CPU to the video card.
     
  11. jpinard

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    What's MAME?
     
  12. K.I.L.E.R

    K.I.L.E.R Retarded moron
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    Multiple Arcade Machine Emulator.
    Missile And Munitions Evaluation.

    Take your pick. ;)
     
  13. mito

    mito beyond noob
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    I've read that "Fast Writes" is not a Radeon friendly option. Is this true for any Radeon? Any drivers? Any config?
     
  14. Star_Hunter

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    Turning off fast writes allowed me to maintain my max oc, when it was on I had to bump the core down to get no artifacts in doom 3.
     
  15. mito

    mito beyond noob
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    Interesting. Please provide us with more details. Your config, clock speeds, etc...

    Thanks.
     
  16. darkblu

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    unavailabilty of fast writes does not preclude the cpu from writing to video memory over the agp bus, it's just that it does so at, erm, unimpressive rates
     
  17. mito

    mito beyond noob
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    Unimpressive rates? Please explain... Danke!
     
  18. Star_Hunter

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    Athlon Xp 1800+ @ 1.84Ghz (11x167) @ 1.7 volt
    ASUS A7v333 (kt333) (card ran at agp 4x since thats max on this mobo)
    Windows XP Pro SP1
    Mushkin Pc2100 512MB(2x256)@ 2.5-3-3-6
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    Sapphire Radeon 9800 NP @ 400/340



    I had to lower the core to 391 to get no artifacts but once I turned off fast writes I was able to go back to 400 (Atitool put my mx oc to 402.5 but I have not tested beyond 400 in doom 3 but I might later...)
     
  19. Guden Oden

    Guden Oden Senior Member
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    AGP1x speed, or ~266MB/s, I believe.
     
  20. mito

    mito beyond noob
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