Graphics vram speeds

[jgunning]

So I have a question lads!

Basically what is the difference between say the GTX 660 192-bit DDR5 and say my card, the Sapphire ATI HD 7870XT Edition 2GB 256-bit DDR5. So the difference I'm asking about is the 192-bit and the 256-bit on each cards.

I understand that they are referring to the bus speeds but still am a bit confused as to what benefits or limitations it can have between the different bus speeds?I have seen many cards with 128-bit, 192-bit, 256-bit etc. But I don't really understand what effect this might have on a card?

Is there a benefit to having the 256-bits on a gfx card rather than the 192-bit? Can someone please help explain this too me?

Cheers Guys!

 

[drdeathx]

http://www.techterms.com/definition/vram

http://en.wikipedia.org/wiki/VRAM

 

[Pinscher]

higher bit bus will give more bandwidth for you vram to take advantage of provided your memory is fast enough to do just that. it is important if you plan to oc your memory and play with a large resolution or multi monitor.

correct me if im wrong

 

[BiggieShady]

Larger VRAM bandwidth is beneficial for multi monitor gaming, screen resolutions 1440p and up and MSAA levels 8x and up.

 

[Mactronix]

Its not the bus speed that those numbers refer to its the width of the bus, or to put it another way how much data it can shift in one go.
Most cards are well optimized to balance out the bus width with a memory speed and thus bandwidth that wont hobble the GPU to less performance than it is ultimately capable of.
Of course this being computers there is as always a BUT here. Companies will use memory bus width to purposely keep a card within a selected price performance section.
Generally the lower the bus the slower you would expect the card to be, again though this is not always the case.
The example you stated is a good one. The 192 bit 660 and the 7870 with its 256 bit bus are pretty much neck and neck depending on the title played.

As said a 256 bit bus will better handle more post processing AA MSAA etc and higher resolution displays.
Mac