high bandwidth memory (HBM)

High Bandwidth Memories(HBM) are memories with high bandwidth. They consist of vertically stacked Dynamic RAMs( DRAM), which are interconnected by means of silicon vias and are used with graphics processors.

High Bandwidth Memories (HBM) have a clock rate of 500 MHz (HBM) or 800 MHz (HBM2) and operate with bus widths of 512 bits (HBM) and 1024 bits (HBM2). The resulting data transfer rate for HBM is 128 GB/s per stack. With four HBM stacks, the memory bandwidth is 512 GB/s. With HBM2 you get values of 1,600 Gbit/s, with four memory stacks the resulting data transfer rate is 6,400 Gbit/s. In contrast, GDDR5 memories have a bus width of 32 bits and a clock rate of 1.75 GHz. The resulting memory bandwidth is 32 GB/s per chip.

In terms of energy consumption, it is lower than that of GDDR5 memories due to the supply voltage of 1.3 V (HBM). In terms of memory bandwidth, the power used for GDDR5 graphics memories is 10 GB/s per watt, which is about three times higher than that of HBM memories. In addition, HBM memories have a much smaller form factor than GDDR5, less than 90% of the GDDR5 form factor. With HBM memories, the interconnect paths and runtimes between the memory stacks and to the GPU are very short, keeping runtime differences low.