ATI Radeon 4870 has double memory bandwidth of 4850
 

The 512Mb GDDR5 chips that ATI uses on its cards with 900MHz frequency have 3.6GB/s throughput or double what would GDDR 3 or 4 have at the same 900MHz speed. You can blame Quad data rate for such a throughput.

ATI’s Radeon HD 4870 512MB card has eight 512Mbit chips on the card while 1GB cards will get the whole sixteen chips, but this will probably happen at some later date due to high cost of GDDR5 memory.

You can see that Radeon HD 4870 will end up with almost twice as much bandwidth than Radeon HD 4850 and we are talking about number close to 115GB/s at least if our math worked well this time.

http://www.fudzilla.com/index.php?op...89&Ite mid=34