How do you calculate memory bandwidth?

[!n$oMniA]

As I understood it, memory bandwidth calulation for a 7800 GT a stock would be:

500 x 3 x 256 = 384000. === (Memory Speed) x (Memeory type (DDR)) x (Memory width)

However on the OcUK web page it is

" - Memory Bandwidth - 32.0GB/sec "

For some reason its driving me insane and I just cant get my head around it.


Thanks in advance for the help,

Andy

 

[oweneades]

Memory speed (1000) x Memory bus width(256) / 8 = 32000 or 32gb/s

(please note the figures in brackets are for the 7800GT)

 

[Phil99]

oweneades is right, but where did the 3 come from? DDR is double data rate, as in 2 x 500 = 1000

 

[sunlitsix]

so this 5600 has only got 8.8gb/s bandwidth?

550 * 128 / 8 = 8800

 

[Phil99]

If the 550 is 275x2, sounds like it, yeah.

 

[oweneades]

so this 5600 has only got 8.8gb/s bandwidth?

550 * 128 / 8 = 8800

Yup sounds about right.