{"id":13595,"date":"2026-10-27T11:00:31","date_gmt":"2026-10-27T03:00:31","guid":{"rendered":"https:\/\/ascentoptics.com\/blog\/?p=13595"},"modified":"2026-10-27T11:02:26","modified_gmt":"2026-10-27T03:02:26","slug":"800g-dac-cable","status":"publish","type":"post","link":"https:\/\/ascentoptics.com\/blog\/800g-dac-cable\/","title":{"rendered":"800G DAC Cable Guide: Specifications, Lengths, and Selection"},"content":{"rendered":"

800G DACs utilize QSFP-DD800<\/u><\/a>\u00a0or OSFP<\/u><\/a>\u00a0form factors and leverage 8\u00d7100G PAM4 technology to achieve 800Gbps transmission; passive DACs can offer power consumption as low as under 0.15W. Due to signal attenuation, the transmission distance for passive DACs at 800G speeds is limited to approximately 2\u20133 meters, while active DACs can extend this range to 5\u20137 meters. When selecting a solution, one must weigh the requirements for ultra-short-reach, low-latency connectivity within a rack against the need for slightly longer-reach connections. Thanks to their low power consumption, low latency, and cost advantages, these cables have become the primary copper-based interconnect solution for linking GPUs to Top-of-Rack (ToR) switches within AI cluster racks.<\/p>\n

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What Is an 800G DAC Cable?<\/strong><\/h2>\n

An 800G DAC cable is a fixed-length copper cable with transceiver-style connectors built onto both ends. It uses twinax copper conductors to move electrical signals directly between two ports, with no optical-to-electrical conversion anywhere in the path.<\/p>\n

The term DAC stands for Direct Attach Copper<\/u><\/a>. Unlike a pluggable optical module that needs separate fiber and cleaning, a DAC is one self-contained assembly. You plug one end into a switch, and the other into a server or another switch, and the link comes up.<\/p>\n

Because the signal stays electrical the whole way, an 800G DAC cable delivers three things optical links struggle to match: the lowest cost per port, the lowest latency, and the lowest power draw. The tradeoff is reach. Copper loses signal integrity quickly, which is why DACs live almost entirely inside a single rack or between adjacent racks.<\/p>\n

Key point:<\/strong>\u00a0An 800G DAC cable is a copper interconnect with no optics. Use it where the link is short and you want minimum cost, latency, and power.<\/p>\n

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800G DAC Specifications and Standards<\/strong><\/h2>\n

An 800G DAC cable<\/a> isn’t a single standard product. It’s a family of cable assemblies that share the same signaling core but vary by form factor, conductor gauge, and whether they include active electronics.<\/p>\n

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Eight Lanes of 100G PAM4<\/b><\/strong><\/h3>\n

At its core, 800G Ethernet is built from eight electrical lanes, each carrying 100 Gbps using PAM4 modulation. The electrical signaling rate is 112 Gbps per lane, which leaves headroom for forward error correction (FEC) overhead on top of the 100 Gbps of usable data.<\/p>\n

The governing standard is IEEE 802.3ck<\/strong>, which defines 800GBASE-CR8<\/strong>\u00a0for copper links. This is the Ethernet baseline. The same physical DAC cables also serve high-speed InfiniBand fabrics up to XDR, so a single cable family can cover both Ethernet switching and AI\/GPU cluster interconnect.<\/p>\n

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Form Factors: OSFP vs QSFP-DD800<\/b><\/strong><\/h3>\n

Two form factors dominate 800G DAC cable assemblies:<\/p>\n