relationship between bus and vram

[MarcuzziAndrea]

Hi,

can someone explain the relation between bus (128, 256 bit) and the amount of vram (2 or 4gb)?

There's a mathematical relationship?

thanks in advance

 

[dish_moose]

2 or 4 - total amount available - pretty self explanatory. The bus width can be visualized as a pipe - larger pipe can carry more at any given pressure(speed). So if you have faster DDR memory working at a faster clock rate - more info (Bytes/s). This gives faster refresh rates - Frames/s FPS.
-Bruce

 

[Kari]

Typically each memory chip uses 32bit bus these days, so on a 128bit card there would be 4 chips, 256bit card needs 8, 384bit 12 and 512bit bus would need a whopping 16 chips.
Also the memory chips themselves come in different sizes, for example 1 gig card with a 128bit bus would need 256MB chips since there is 4 of them, and to get 4gigs of ram on a 256bit bus you'd need chips with 512MB on each of them.

so it's pretty simple

 

[MarcuzziAndrea]

Typically each memory chip uses 32bit bus these days, so on a 128bit card there would be 4 chips, 256bit card needs 8, 384bit 12 and 512bit bus would need a whopping 16 chips.
Also the memory chips themselves come in different sizes, for example 1 gig card with a 128bit bus would need 256MB chips since there is 4 of them, and to get 4gigs of ram on a 256bit bus you'd need chips with 512MB on each of them.

so it's pretty simple

ok, man thank u. 32bit for every chip sure? nvidia, for example, use 512 chip in gtx 770 4gb (8 chip 512 mb)?

@dish: thank u dish

http://extremespec.net/msi-release-geforce-gtx-770-gaming-4gb-oc/

http://www.samsung.com/global/business/semiconductor/file/product/graphic_product_guide_nov_12-0.pdf

 

[Kari]

ok, man thank u. 32bit for every chip sure? nvidia, for example, use 512 chip in gtx 770 4gb (8 chip 512 mb)?

@dish: thank u dish

http://extremespec.net/msi-release-geforce-gtx-770-gaming-4gb-oc/

http://www.samsung.com/global/business/semiconductor/file/product/graphic_product_guide_nov_12-0.pdf

yeah, the pic of the card shows 8 vram chips around the gpu, so those would be 512MB chips.
The Samsung memory guide uses bits rather than bytes so the 512MB components are marked as 4Gb. (1B=8b)