Comment by bob1029

5 hours ago

It's not that there's a blocker. It's that it takes roughly 3x the manufacturing capacity to produce an HBM package at the same storage capacity as DRAM. We are sacrificing total bytes for bandwidth.

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bob1029

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rkagerer  3 hours ago

I don't fully understand the source of the "total bytes" constraint, but a major factor may be because HBM4 / HBM4E can only make use of the footprint directly above the processor/logic die (or in direct vicinity of its interconnect), while traditional DRAM can be placed further away where there's lots of real estate on the motherboard.

I gather a practical max ceiling today is a stack of 16 chips in height yielding 64GB?

These chips have a massive bus size of 2048 bits, instead of the 64 or 128 bits (dual channel) used by DDR5. That's what gives them their order-of-magnitude bandwidth speedup. But even though they technically pack in more capacity per square millimeter of motherboard, I gather they take up more space than older technologies once you account for the vias and interconnects to route all those signals.

  • threecheese  2 hours ago

    Thanks for that, just went down an interesting rabbit hole. Many of us were hoping this re-tooling would eventually trickle some fast RAM down to DRAM-exhausted PCs, but given it would require a rearchitecture of the motherboard it's unlikely.

    • sroussey  1 hour ago

      HBM also trades bandwidth for latency, and your regular computing is much more sensitive to latency than bandwidth.

tliltocatl  5 hours ago

How so? FEOL is pretty much the same, BEOL is almost the same save TSVs, the packaging tech is different and more advanced, but not exactly 1:1 comparable. Do TSVs really occupy 3x the area of DDR IO's?