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shadizzle

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    shadizzle reacted to Kuzma in Memory Bus size and how it effects your VRAM usage   
    Introduction:
    You may have seen me post around quite a bit telling people not to buy the 4GB variants of the 760, 770, 660 TI or 680 or the 6GB variant of the 7970; this is due to a little factor called the memory bus size it's hard to explain it on a technical level while still making it easy to understand so I'll simplify it down to a real world analogy.
     
    What exactly is the memory bus?
    The memory bus is the pathway that your gpu uses to access the memory it has and is generally measured in bits (8 bits = 1 byte :P ) this works together with the memory clock speed to work out exactly how much of the memory can be accessed per second.
     
    So how will it effect my graphics card?
    Think of the memory as water and the memory bus as a tunnel, if you need more water than your memory bus will let through then you're going to have to wait a while to wait for that extra water to come through. If your graphics card has memory bus designed for 2GB and your add another 2GB then you've added more water without being able to get that extra water through the memory bus.
     
    What about memory clock?
    The memory clock is like the speed of the water, if you increase the speed of the water enough then you can push more water through the small memory bus ^_^ the issue is however that you need a pretty large speed increase to access double the water in comparison to before.
     
    Conclusion
    So if you're buying a variant of a graphics card with double the memory then make sure that either the memory clock is increased or you know you'll be able to increase it (gpu boost 2.0) otherwise all that extra memory (and that extra cash) is wasted. Since memory clocks generally aren't very very high a good rule of thumb is 128bits and 1000mhz effective memory clock per gb (this can change to 64bits and 2000mhz and vice versa so make sure you do your math :D to work out if you're going to be able to use all that memory)
     
    P.S.
    I thought I'd add in my Titan calculations for any of you mathematicians reading this (attatched as a txt) and by my calculation a titan would need exactly double it's effective memory clock speed to access all 6GB of it's memory that or it's only accessing 3GB of it's memory and since we've already seen the titan use more than that leaving me with the conclusion GK110 only needs half the memory clock to access all the GB which to me is a crazy revolutionary advancement O.o
    titan calculations.txt
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