weird in a sense that it didn't follow the usual config on most cards but whatever hehe. If i understand correctly, 550 Ti's config is like:
3GB on a 384bit bus would prolly give similar config to custom 3GB GTX 580.
256MB x 12 chips, each chip would be 32bit wide, each chip would have of uh... assuming 32 ROPs, how would you divide that with 12 memory chips? '__'