Each full fledged GV100 GPU contain 8 512-bit memory controllers. 2 MCs are connected to 1 HBM2 stack, making 4 HBM2 stacks (4GB each). For Titan V, one of the MC is disabled making the interface from 4096 to 3072-bit. Also, 1024MHz can’t be achieved on HBM2 so, the total bandwidth possible is just 900GBps (< 4096bit * 1024MHz).
Source: Deep Learning on Medium