As data centers and HPC systems continue to scale in speed and capacity, the demand for high-speed, reliable, and thermally efficient interconnects is growing rapidly. Among various form factors, the OSFP flat-top DAC cables have drawn attention for their compact structure and thermal efficiency in dense computing environments. This article will introduce the key features of high-speed OSFP flat-top DAC cables and their applications in NVIDIA DGX H100 systems.
OSFP Flat-top DAC Cables: Overview and Key Features
OSFP flat-top DAC cables are engineered to meet the demanding connectivity requirements of HPC clusters and dense data center deployments, supporting transmission rates up to 400G, 800G, and 1.6T. Their slim, finless design maximizes direct contact with connected devices, improving heat dissipation and enhancing transmission stability.
By eliminating the external fins used in conventional designs, the OSFP flat-top DAC cables structure enables tighter port spacing, simplifies installation in high-density racks, and reduces dependence on external cooling airflow. The result is a more space-efficient and cost-effective interconnect solution that maintains stable transmission even under high thermal loads.
OSFP Flat-top VS. Finned-top DAC Cables: Distinctions
OSFP flat-top and finned-top DAC cables offer three distinct solutions for high-speed interconnects. Understanding their differences in physical structure, thermal management, and applications helps better evaluate their characteristics and select the most suitable cable type for specific deployment needs.
OSFP flat-top DAC cables primarily dissipate heat by increasing contact with the device. They are typically deployed with OSFP ConnectX-7 NICs utilizing cage-riding heat sinks or DGX H100 Cedar7 GPU employing internal cage-riding, air-cooled heat sinks in liquid-cooled systems. For example, 400G OSFP flat-top DAC cables are used with ConnectX-7 NICs, and 800G OSFP flat-top DAC cables are for DGX H100 systems.
In contrast to OSFP flat-top DAC cables, OSFP finned-top DAC cables feature heat-dissipation fins and are divided into open-top (commonly referred to simply as "finned-top") and closed-top types. The open finned-top relies on air convection, making it suitable for air-cooled switches and. The closed finned-top incorporates a metal cover over the fins, which merges the cooling benefits of both finned-top and flat-top designs, enabling deployment in both air-cooled switches and liquid-cooled systems, providing distinct deployment flexibility.
The comparison below summarizes their respective differences in physical structure, thermal management and application scenarios.
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Features
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OSFP Flat-top DAC
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OSFP Finned-top DAC
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OSFP Closed Finned-top DAC
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Physical Structure
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Compact
Smooth surface
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Thicker, Heat dissipation fins
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Thicker
Heat dissipation fins
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Thermal Management
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Increases the contact area with devices
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Utilizes air convection
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Combines the cooling characteristics of both the finned top and flat top.
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Applications
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ConnectX-7 adapters (400G)
DGX H100 Cedar7 GPU (800G)
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Air-cooled switches
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Air-cooled switches
Liquid-cooled Systems
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Compared to OSFP finned-top and closed-top DAC cables, OSFP flat-top DAC cables are thinner and easier to integrate into dense server and switch environments, achieving plug and play. For advanced setups such as ConnectX-7 adapters or DGX H100 Cedar7 GPU systems, OSFP flat-top DAC cables provide reliable operation, optimized thermal performance, and overall cost-efficiency, supporting more streamlined and scalable network deployment.
OSFP Flat-top DAC Cables: DGX H100 Case
The NVIDIA DGX H100 is the core computing platform for enterprise AI and HPC infrastructures. With eight H100 Tensor Core GPUs connected through fourth-generation NVLink, it delivers extreme compute density for large-scale model training and simulation, driving massive GPU-to-GPU data traffic that demands ultra-low-latency, high-bandwidth interconnects. Each DGX H100 integrates four twin-port OSFP flat-top cages, where each 800G cage connects two 400G ConnectX-7 NICs on internal Cedar7 cards. This 2x400G configuration provides 800G aggregate bandwidth per cage, ensuring full GPU communication throughput. The flat-top design is required because it fits the 800G cages with internal, air-cooled riding heat sinks in DGX systems, while finned-top modules or DAC cables are not supported. The 800G OSFP flat-top DAC cable provides an ideal solution for the DGX H100, enabling DGX H100 to maintain efficient, reliable, and compact connectivity. This design reduces redundant PCBs and cages, optimizes thermal and space performance, and ensures consistent high-speed transmission across InfiniBand and Ethernet fabrics, supporting stable large-scale AI cluster operation. Compared to optical modules, the solution simplifies cabling and reduces power consumption.
Conclusion
With their compact design, easy deployment, reliable thermal management, and efficient performance, OSFP flat‑top DAC cables provide strong support for scalable networks in HPC and data centers. These advantages position them as a key enabler for future network architectures as data centers demand for speed and density grow.
