HBM (High Bandwidth Memory)
Beginner
Memory chips stacked into a tower right next to the main chip. Thousands of tiny wires link them, so data flows very fast.
Novice
A tower of DRAM memory chips stacked on top of each other and connected by vertical metal holes through the silicon. It sits beside the processor in the same package and talks to it over a very wide connection, about a thousand wires or more.
Expert
JEDEC-standard stacked DRAM with a 1,024-bit (HBM3) or 2,048-bit (HBM4) interface per stack, wired through an interposer or bridge. The PHY on the processor die, the interposer routing and heat flowing between logic and DRAM all constrain the floorplan.
Explained in AI accelerators and datacenter (Industries).