Welcome!

 Three months have somehow flown by since I left TechInsights, which acquired The Linley Group in October 2021. I've been able to mix some personal travel and urgent customer projects, but now it's time to reconnect with all of you. Please watch this space for news and analysis from the worlds of networking, data centers, and semiconductors.


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AMD Looks to Infinity for AI Interconnects

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With the formal launch of the MI300 GPU, AMD revealed new plans for scaling the multi-GPU interconnects vital to AI-training performance. The company's approach relies on a partner ecosystem, which stands in stark contrast with NVIDIA's end-to-end solutions. The plans revolve around AMD's proprietary Infinity Fabric and its underlying XGMI interconnect. Infinity Fabric Adopts Switching As with its prior generation, AMD uses XGMI to connect multiple MI300 GPUs in what it calls a hive. The hive shares a homogeneous memory space formed by the HBM attached to each GPU. In current designs, the GPUs connect directly using XGMI in a mesh or ring topology. Each MI300X GPU has up to seven Infinity Fabric links, each with 16 lanes. The 4th-gen Infinity Fabric supports up to 32Gbps per lane, yielding 128GB/s of bidirectional bandwidth per link. At the MI300 launch, Broadcom announced that its next-generation PCI Express (PCIe) switch chip will add support for XGMI. At last October'
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NVIDIA Networks NVLink

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I attended several sessions at last week's Hot Chips, and NVIDIA's NVSwitch talk was a standout. Ashraf Eassa did a great job of covering the talk's contents in an NVIDIA blog, so I will focus on analysis here.  SuperPOD Bids Adieu to InfiniBand From a system-architecture perspective, the biggest change is extending NVLink beyond a single chassis. NVLink Network is a new protocol built on the NVLink4 link layer. It reuses 400G Ethernet cabling to enable passive-copper (DAC), active-copper (AEC), and optical links. The build its DGX H100 SuperPOD, NVIDIA designed a 1U switch system around a pair of NVSwitch chips. The pod ("scalable unit") includes a central rack with 18 NVLink Switch systems, connecting 32 DGX H100 nodes in a two-level fat-tree topology. This pod interconnect yields 460.8Tbps of bisectional bandwidth. NVLink Network replaces InfiniBand (IB) as the first level of interconnect in DGX SuperPODs. The A100 generation pod uses an IB HDR leaf/spine inte
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NVIDIA Reveals DGX GH200 System Architecture

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We industry analysts sometimes get out over our skis when trying to project details of new products. Following NVIDIA's DGX GH200 announcement at Computex, we noticed industry press making the same mistake. Rather than correct our previous NVLink Network post, we'll explain here what we've since learned. Our revelation came when NVIDIA published a white paper titled NVIDIA Grace Hopper Superchip Architecture . The figure below from that paper shows the interconnects at the HGX-module level. The GPU (Hopper) side uses NVLink as a coherent interconnect, whereas the CPU (Grace) side uses InfiniBand, in this case connected through a Bluefield-3 DPU. From a networking perspective, the NVLink and InfiniBand domains are independent, that is, there is no bridging between the two protocols. HGX Grace Hopper Superchip System With NVLink Switch (Source: NVIDIA) The new DGX GH200 builds a SuperPOD based on this underlying module-level architecture. You've probably seen the headlin
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