AMD’s Helios rack uses 72 MI455X GPUs and 260 TB/s of scale-up bandwidth

SumitGup · x · 2026-07-25

AMD's Helios rack-scale platform ties 72 MI455X GPUs into one shared-memory system

The post breaks down AMD’s Helios rack-scale AI architecture, which uses 72 MI455X GPUs, 12 Broadcom Tomahawk 6 ASICs, and 36 parallel network planes to deliver 3.6 TB/s bidirectional bandwidth per GPU and 260 TB/s aggregate scale-up bandwidth.

UALoE defines GPU-to-GPU communication semantics, including memory reads and writes, ordering, and traffic distribution across the 36 planes.
ESUN provides the Ethernet fabric underneath, handling forwarding, flow control, congestion management, retries, and small-message transport.
The result is a rack where 31 TB of HBM4 remains physically distributed but can be accessed as if the whole cabinet were a single tightly coupled computer.

The image also shows the scale-up architecture as an Ethernet-based stack built around UALoE, OCP SUE, and ESUN, with AMD, Broadcom, Cisco, Meta, Microsoft, NVIDIA, and others listed as founding members.

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AMD’s Helios rack uses 72 MI455X GPUs and 260 TB/s of scale-up bandwidth

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