Question : Problem: Data Width?

I have encountered this terminology on numerous occasions, when in the current process of purchasing a GPU - what does its meaning denote?

Moreover, I found it to be existent in two variants: 128/256-bit.

Answer : Problem: Data Width?

Memory bus width is part of the total equation of how much memory bandwidth you can get, to transfer video data like textures - the other factors are clock speed and whether you use DDR to take advantage of rising and falling edges of signals.

http://www.hardwarecentral.com/hardwarecentral/reports/2243/3/