Presidium :
pasow :
bandwidth is a relation of the clocking speed, bus width, and memory type. the amount of it is inconsequential to its bandwidth so long as its quantity is a power of its bus width. otherwise you end up with these weird performance differences like Nvidia is currently in litigation over on its 970.
generally the hierarchy is, memory type > bus width > clocking speed.
edit...
it looks like the R9 270x is around 10% faster than the R9 270 with the same quantity of memory.
So is there a calculation that you can do on the GPU's specs (like memory amount X clock speed X bus width, or something like that) so get a general sense of the amount of throughput you get?
Basically, I'm wondering how "throughput" is calculated. If a card with DDR3 RAM has the same throughput as a card with GDDR5 RAM, is there a difference beside being able to say that the second GPU has "better" RAM?
Well the (hypothetical) GDDR5 card would have a much smaller memory bus than the DDR3 card if they had similar bandwidth, so the GDDR5 card would likely use significantly less power.
Also, you have to consider compression these days. Nvidia manage to avoid using large power hungry memory busses on modern cards due to some clever colour compression, which effectively increases the "bandwidth" by using the GPU power to reduce the amount of memory bandwidth used.