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
而就目前來看GDDR5已經跟不上時代的發展了，於是出現了HBM、HBM2、GDDR5X。那麼什麼是HBM呢？HBM（High Bandwidth Memory ）是一款新型的CPU/GPU 內存芯片（即 “RAM”），其實就是將很多個DDR芯片堆疊在一起後和GPU封裝在一起，實現大容量，高位寬的DDR組合陣列。第一代HBM每個Die容量可達2GB，帶寬128GB/s，總線位寬高達1024-bit。要知道GDDR5位寬僅有28GB/s總線位寬僅有32-bit，效率是GDDR5的三倍，PCB面積比GDDR5少94%。第二代HBM更加恐怖，每個堆棧的帶寬翻番爲256GB/s，每個Die的容量達到8Gb，而每個堆棧能容納最多8個Die，一顆GPU核心搭配四個HBM2堆棧，那麼顯存容量將最高可達32GB，帶寬則可達1TB/s，1TB/s啊！至於GDDR5X，則是由於HBM產能不足出現的過渡產品，大部分人對GDDR5X可能比較熟悉，英偉達把它用在了GTX1080、GTX1080Ti、Titan xp上，位寬256-bit總帶寬達到320GB/s。