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Video card buses?

Discussion in 'Graphics Cards' started by binsky3333, Feb 25, 2008.

  1. binsky3333

    binsky3333 New Member

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    Hi,
    I just have a quick question about video card buses. Is the bigger the bus the better?
    Would a 320bit bus be better than a 256bit bus.
  2. hat

    hat Maximum Overclocker

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    NO. Actually in my mind 320 bit is WORSE cause 320 bit is actually a 256-bit bus and a 128-bit bus on the same card. 320-bit is actually a 256-bit bus and a 64-bit bus togeather. Stick with doubles, as in 128, 256, 512, etc...
    Crunching for Team TPU
  3. binsky3333

    binsky3333 New Member

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    But is a bigger bus better? (doubles) or the lower the bus better?
  4. W1zzard

    W1zzard Administrator Staff Member

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    sorry thats bs
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  5. W1zzard

    W1zzard Administrator Staff Member

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    a wider bus is always better as long as you stay within the same architecture. a wider bus has always more potential independant of architecture, but the real performance also depends on the memory controller implementation when comparing say g80 to r600

    each single memory chip has a certain bus width. all chips combined form a datapath. for example ten chips at 32 bits = 320 bits (8800 GTS G80 based). the 8800 GS uses 64 bit but only 5 chips = 384 bit

    [​IMG]
    when you look at the g80 architecture you see 6 ROP partitions (FB). each partition has a 64 bit wide memory interface to the dram pool
    Last edited: Feb 25, 2008
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  6. hat

    hat Maximum Overclocker

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    It's not really two seperate busses? That's just what I read here... thanks for clearing that up.
    Crunching for Team TPU
  7. W1zzard

    W1zzard Administrator Staff Member

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    where did you read that?
  8. hat

    hat Maximum Overclocker

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    Don't remember. Somewhere on here... I'd have to look but I don't even remember what the thread was about.
    Crunching for Team TPU
  9. binsky3333

    binsky3333 New Member

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    So a 320bit is better than a 256bit thx for the help!!
  10. Mussels

    Mussels Moderprator Staff Member

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    w1zz saves the day!

    Your question is obviously about the 8800GTS.
    Two models exist: G80 and G92.

    G80 has a 320bit bus and 640MB of ram
    G92 has a 256 bit bus, and 512MB of ram

    Normally if it was a direct comparison, the 320 bit bus would be the obvious winner - its got more bandwidth for the ram to use... but the G92 core on the 512MB card, is quite improved.

    Its a toss up - faster core, or faster ram? Overall the faster core (G92) version is the winner, moreso because it uses less power, therefore it runs a lot colder and quieter than the older, G80 version.

    A good example of this, is that my (heavily overclocked) 8800GT (256 bit bus) can! be faster than my 8800GTX (384 bit bus) at lower resolutions. Its higher clock speed gives it a pixel shader boost, but at higher resolutions (1680x1050 and up) the GTX shines and destroys the GT.
  11. hat

    hat Maximum Overclocker

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    Yeah, just the memory bus though. The 256-bit 8800GTS is still faster, just cause it's a faster card.
    Crunching for Team TPU
  12. binsky3333

    binsky3333 New Member

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    On the picture where are the 10 32bit memory chips.
  13. W1zzard

    W1zzard Administrator Staff Member

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    not drawn in the architecture image.. pics there http://www.digit-life.com/articles2/video/g80-2.html

    its a bit similar to a highway .. if you have not many cars on the road there is almost no benefit from going to 4 lanes or more. in heavy traffic such an improvement can make quite a difference. another important factor is how skillful the drivers are (that would be the memory controller architecture). how fast the cars go is the memory clock. memory latencies would affect how close behind each other the cars can drive
  14. Mussels

    Mussels Moderprator Staff Member

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    the G80 core was used in the original GTS and the GTX and ultra cards. I dont know what version his pic is of, or if it even shows that - remember that these things are grouped together, his image may only show the groups.
  15. binsky3333

    binsky3333 New Member

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    Where can i find architecture images for all of the cards. (g80, g92)
  16. DanTheBanjoman Señor Moderator

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    A wider bus allows more data to be sent at the same time. So at the same clock a wider bus has the advantage. However the wider the bus the harder it is to sync them and interference may become an issue as well. ie it becomes harder to clock as high.
    For this very reason we moved from parallel ATA to serial ATA and from parallel PCI to serial PCI express. So when picking a video card a wider bus is usually better, assuming the difference in bus width is bigger than the difference in clock. When you buy a card syncing isn't the issue since the manufacturer already made it work for you.
    Additionally higher clocks result in lower latencies, which could also be worthwhile in various scenarios.
  17. W1zzard

    W1zzard Administrator Staff Member

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    google :p
  18. binsky3333

    binsky3333 New Member

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    OK now one more question, is it better for my bandwidth on my video card to be higher. Which is a better OC core or memory. (memory increases bandwidth)
  19. binsky3333

    binsky3333 New Member

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    we should sticky this post it could be helpful to other people!
  20. Mussels

    Mussels Moderprator Staff Member

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    all of them are important. Thats why we read wizzards reviews, to see what happens - theres more to it than just those, despite the fact the GTS GTX and ultra are all G80 cores, they also vary how many shaders they have and so on.

    Thats why we read the reviews wi1zz writes, cause you cant really guess how well a card is balanced til someone tries it!
  21. W1zzard

    W1zzard Administrator Staff Member

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    oc both as far as you can go. usually one overclock will affect the other, so you cant maximize both. only way to know is by running benchmarks. personally i would say it will not matter for general use, better to have a stable system.
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  22. hat

    hat Maximum Overclocker

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    Generally overclocking the memory is more important unless you got a slow core (under 500MHz) and fast memory (GDDR4)
    Crunching for Team TPU
  23. largon New Member

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    I'd imagine one thread about the subject would be enough...
  24. Voice-Of-Palit

    Voice-Of-Palit Palit Representative

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    To clarify: Throughput is the number you want. How much stuff can you get from one side to the other. This is generally measured in bandwidth. While theoretical and actual vary, the more the better.

    So how do you get more through? Frequency and bus width.

    If you have 2 buses that are 128 bit and one is running at 500 MHz and the other is at 450 MHz, you will have more bandwidth on the one at the higher clock speed.

    Let's do this again but with 2 buses with different widths, 128 and 256. If the 128-bit bus is operating at 700 MHz and the 256-bit is at 350 MHz, it is a theoretical tie. However, there might be a slight advantage in the real world for the 256-bit bus as real bandwidth and theoretical are never the same.

    That being said, go for cards that have higher memory frequencies (the bus will operate at that clock domain) as well as have a wider bus.
    Mussels says thanks.
  25. Mussels

    Mussels Moderprator Staff Member

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    summary: if you can get the same card, but the bus caries (cheap cards do this, especially between DDR2 and DDR3 models) grab the larger one. When it comes to higher end cards, read reviews - too much else is at stake to judge it by the one feature alone.

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