Derived from the GDDR5 SGRAM JEDEC standard, GDDR5X specifies key elements related to the design and operability of memory chips for applications requiring very high memory bandwidth. With the intent to address the needs of high-performance applications demanding ever higher data rates, GDDR5X is targeting data rates of 10 to 14 Gbps, a 2X increase over GDDR5. In order to allow a smooth transition from GDDR5, GDDR5X utilizes the same, proven pseudo open drain (POD) signaling as GDDR5.
GDDR5X will deliver 64B data per memory access to the memory cells, doubling from the 32 byte/access offered by GDDR5. The 16n prefetch allows GDDR5X to explore new horizons for discrete memory I/O data rates. Initial target is 10-12GBps, potentially reaching the 14 or even 16 Gbps.
High-end graphics cards currently hover at say 400 GB/s. With GDDR5X that could increase to 800~1000 GB/sec and thus these are very significant improvements, actually they are competitive enough with HBM memory that AMD right now uses on their latest GPUs.