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The initial specification defines HBF packages with capacities of up to 512GB using either 8-Hi or 16-Hi NAND die stacks, though these will not be standard 3D NAND stacks, but rather specialized devices with a fast interface. In fact, Sandisk once called them HBF core dies rather than 3D NAND die stacks.
Performance of HBF is divided into three bandwidth grades ranging from approximately 0.4 TB/s to 3.0 TB/s (though we are not sure whether this figure describes the full HBF subsystem or per-package bandwidth). Such a huge performance range implies that Sandisk and SK hynix expect HBF to have a multi-year roadmap featuring multiple implementations and generations of HBF. It is noteworthy that the most capable implementation of HBF (3 TB/s) is set to beat the memory bandwidth of a single HBM4 memory stack (2 TB/s), though it will be unlikely to beat HBM4 when it comes to latency.
Interestingly, SK hynix claims that HBF uses the Universal Chiplet Interconnect Express (UCIe) standard to simplify integration with heterogeneous computing platforms, whereas Sandisk claims that HBF is set to adopt the 'xPU-HBF' interface, which could be its definition of UCIe implemented by companies like Broadcom or Marvell.
In addition to capacity and performance targets, the specification establishes electrical and interface characteristics, packaging and reliability guidelines for stacked HBF devices, as well as software I/O requirements. For now, these specifications are not officially published by the OCP.
Nvidia and SK hynix ink multi-year memory co-development and supply agreement
Key considerations
- Investor positioning can change fast
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Reference reading
- https://www.tomshardware.com/pc-components/ssds/SPONSORED_LINK_URL
- https://www.tomshardware.com/pc-components/ssds/sandisk-and-sk-hynix-unveil-hbf-spec-up-to-16-hi-nand-stacks-3-tb-s-bandwidth-ucie#main
- https://www.tomshardware.com/membership
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