High Bandwidth Memory (HBM)
High Bandwidth Memory is a high-performance RAM interface for 3D-stacked SDRAM from Samsung, AMD and SK Hynix. It is used in conjunction with high-performance graphics accelerators and network devices. The first HBM memory chip was produced by SK Hynix in 2013, and the first devices to use HBM were the AMD Fiji GPUs in 2015. High Bandwidth Memory has been adopted by JEDEC as an industry standard in October 2013.
HBM achieves higher bandwidth while using less power in a substantially smaller form factor than DDR4 or GDDR5. This is achieved by stacking up to eight DRAM dies (thus being a Three-dimensional integrated circuit), including an optional base die with a memory controller, which are interconnected by through-silicon vias (TSVs) and microbumps.
HBM memory bus is very wide in comparison to other DRAM memories such as DDR4 or GDDR5. An HBM stack of four DRAM dies (4‑Hi) has two 128‑bit channels per die for a total of 8 channels and a width of 1024 bits in total. A graphics card/GPU with four 4‑Hi HBM stacks would therefore have a memory bus with a width of 4096 bits. In comparison, the bus width of GDDR memories is 32 bits, with 16 channels for a graphics card with a 512‑bit memory interface.