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Thread: AGP Compatibility

  1. #1
    Administrator Steve R Jones's Avatar
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    AGP Compatibility

    AGP Compatibility
    http://www.ertyu.org/~steven_nikkel/...atibility.html


    Speed is always backwards compatible,
    for example, a 4x device must be able to run at 2x and 1x.


    The signalling voltage is the only incompatible part.


    An 8x device must be 0.8v,
    a 4x device can be 1.5v or 0.8v,
    a 2x or 1x device can be 3.3v or 1.5v.



    AGP Connectors

  2. #2
    Ultimate Member gjimene2's Avatar
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    Great info Steve!

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    Substantial bits of it wrong, though. AGP 1x and 2x modes _always_ are 3.3V signalling. Cards do not HAVE to be backward compatible (sole exception: 8x gear must be backward compatible to 4x). There is no such thing as "Universal AGP 1.5V" since "Universal" implies 3.3V signalling support.

    In other words, 1x and 2x modes always are 3.3V signalling, 4x is 1.5V, 8x is 1.5V with reduced swing (0.8V).

  4. #4
    The Burninator sm8000's Avatar
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    Of the AGP Pro slots pictured, which is "50" and which "110"? And what do those designations mean?

  5. #5
    Ultimate Member cbh's Avatar
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    But an 8x card can be installed on a 4x AGP slot?? Is that possible?
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  6. #6
    The Burninator sm8000's Avatar
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    Yes. By the AGP 3.0 standard's definition, 8x hardware must be able to run on a 4x slot (at 4x speed) and vice versa - an 8x slot must allow a 4x card to run on it (also at 4x speed).

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    I agree that a X8 will run in a x4 system any day .
    Another thing is a x4 running in a x2 or x1 AGP.Not allways.
    The theory says yes and for what I've seen......may be.

  8. #8
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    Whether or not an 8x/4x card runs in a 2x/1x slot depends on whether it still supports 3.3V signalling as well. In other words, if it's keyed "universal", it should. If it's keyed 1.5V-only (like the Radeon 9600 series and recent 9800XT/SE models), it doesn't even fit, let alone work.

    On top of that, one thing that keeps new cards from working in old boards is power consumption. AGP standard, revision 2.0, has a much higher power budget than the original AGP 1.0 specification. (Don't confuse with 1x and 2x transfer modes please!). So if your mainboard is AGP 1.0, you'll need to choose a card that doesn't have too high a power consumption - or one that uses a separate power cable anyhow.

  9. #9
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    Originally posted by cuelebre
    I agree that a X8 will run in a x4 system any day .
    Another thing is a x4 running in a x2 or x1 AGP.Not allways.
    The theory says yes and for what I've seen......may be.
    In some cases you can 'if' your bios allows for raising agp voltage, and 'if' he rails on your PSU are speced and steady. Also of note higher end cards that need a molex connection basically need the juice from your PSU, so you need a good power supply. Good sticky there Peter-

  10. #10
    Ultimate Member cbh's Avatar
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    I'm using a Intel D845PESV deskboard and I don't know whether it can support an 8x AGP card.

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  11. #11
    The Burninator sm8000's Avatar
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    Look it up at intel.com - if it says it can support 4x, then any 8x card will work.

  12. #12
    Member cjmunroe's Avatar
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    agp 8x 3.0

    OK so, I have a motherboard that says it supports 8X 3.0, but only 1.5 v cards. I have a geforce fx5600, which is also an agp 8X 3.0 card, but does signalling volatge at 0.8 v mean it wont run at 8X with the 1.5 v requirement of my motherboard? I find this stuff so confusing. thx in advance.

  13. #13
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    As I said further above already, _all_ 8x cards do 1.5V signalling - only with reduced voltage swing. This is often falsely referred to as 0.8V signalling. It is not.

    8x and 4x hardware must, by the AGP standard, be inter-operable. Only when you cross the 2x/4x threshold, you'll have to watch things. Again, see above.

  14. #14
    Member cjmunroe's Avatar
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    Sorry, I've always been confused about that. Thanks for finally making it clear -- it seems nobody else can.

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    Quote Originally Posted by cbh
    But an 8x card can be installed on a 4x AGP slot?? Is that possible?
    I always thought that I could not put an 8X agp card into my 2.0 slot which is a 4x agp. Does this mean that all 8X video cards will work or only those specified as 8x/4x?
    I want to replace and upgrade from a GeForce2 MX400 4x/2x 64MB card. Can I really put in an 8X card? or do have to look for the 4X? any advice for this not so savy computer user

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