ATI 4770 has a bus of only 128bit, BUT the memory is GDDR5 which makes up for the bandwidth, making the card almost equal with ATI 4850 (258bit + GDDR3). 128bits =/= 128 MB of memory. The 128 bits is the width of the bus which carries information from the CPU to the graphics card (I suggest a little reading into the matter). Coupled with the fast GDDR5 memory, the 128 bit bus will be enough for any current game(medium-high details), giving you 2-3x times the performance of 3850 at any resolution, even with only 512 MB of memory. If you can get a 4770 with 1GB of memory at a good price, that is the card I suggest you to buy, otherwise search for a 4770 with 512MB. If the cards are too expensive buy the 3850.