https://www.amd.com/en/technologies/hbm
https://www.amd.com/system/files/documents/high-bandwidth-memory-hbm.pdf
HBM is a new type of CPU/GPU memory (“RAM”) that vertically stacks memory chips, like floors in a skyscraper. In doing so, it shortens your information commute. Those towers connect to the CPU or GPU through an ultra-fast interconnect called the “interposer.” Several stacks of HBM are plugged into the interposer alongside a CPU or GPU, and that assembled module connects to a circuit board.
Though these HBM stacks are not physically integrated with the CPU or GPU, they are so closely and quickly connected via the interposer that HBM’s characteristics are nearly indistinguishable from on-chip integrated RAM.
https://baijiahao.baidu.com/s?id=1595108404131780055&wfr=spider&for=pc
而就目前来看GDDR5已经跟不上时代的发展了，于是出现了HBM、HBM2、GDDR5X。那么什么是HBM呢？HBM（High Bandwidth Memory ）是一款新型的CPU/GPU 内存芯片（即 “RAM”），其实就是将很多个DDR芯片堆叠在一起后和GPU封装在一起，实现大容量，高位宽的DDR组合阵列。第一代HBM每个Die容量可达2GB，带宽128GB/s，总线位宽高达1024-bit。要知道GDDR5位宽仅有28GB/s总线位宽仅有32-bit，效率是GDDR5的三倍，PCB面积比GDDR5少94%。第二代HBM更加恐怖，每个堆栈的带宽翻番为256GB/s，每个Die的容量达到8Gb，而每个堆栈能容纳最多8个Die，一颗GPU核心搭配四个HBM2堆栈，那么显存容量将最高可达32GB，带宽则可达1TB/s，1TB/s啊！至于GDDR5X，则是由于HBM产能不足出现的过渡产品，大部分人对GDDR5X可能比较熟悉，英伟达把它用在了GTX1080、GTX1080Ti、Titan xp上，位宽256-bit总带宽达到320GB/s。