800G DAC Cable for Nvidia DGX & HGX: Specs & Sourcing Guide

When building Nvidia DGX H100, DGX H200, or HGX-based AI clusters, the interconnect cable between GPUs, NICs, and top-of-rack switches is a critical but often overlooked decision. The wrong cable choice leads to link failures, insertion loss errors, or incompatibility issues discovered only after deployment. This guide covers everything procurement teams and network engineers need to know about 800G DAC cables for Nvidia AI infrastructure.

What Is an 800G DAC Cable?

A Direct Attach Copper (DAC) cable is a fixed-length assembly consisting of a copper cable with transceivers permanently attached at both ends. The 800G variant uses QSFP-DD (Quad Small Form-factor Double Density) or OSFP connectors and supports 8x100G NRZ or 4x200G PAM4 electrical signaling to achieve 800 Gbps aggregate throughput.

For Nvidia DGX systems, DAC cables are the standard choice for short-reach connections (0.5m-3m) between:

GPU nodes to top-of-rack (ToR) switches
NVLink switch to compute nodes
Spine-to-leaf switch connections within the same rack

800G DAC Cable Specifications for Nvidia Platforms

Parameter	QSFP-DD 800G DAC	OSFP 800G DAC
Form Factor	QSFP-DD (SFF-8665)	OSFP (SFF-8972)
Data Rate	8x100G NRZ / 4x200G PAM4	8x100G NRZ / 4x200G PAM4
Max Reach	3m passive / 5m active	3m passive / 5m active
Power Consumption	<2.5W (passive)	<3.5W (active)
Connector	QSFP-DD both ends	OSFP both ends or breakout
Compatible Switches	Nvidia Quantum-2, Arista 7060	Nvidia Quantum-2, Cisco 8000
Cable Gauge	26-30 AWG twinax	26-30 AWG twinax
Operating Temp	0°C to 70°C	0°C to 70°C
RoHS Compliant	Yes	Yes

Nvidia DGX Compatibility Guide

Each Nvidia DGX/HGX generation uses specific connector types. Ordering the wrong form factor is the most common procurement mistake:

Platform	NIC/Switch Port	Required DAC Type	Recommended Length
DGX H100	ConnectX-7 (QSFP112)	QSFP-DD 800G Passive DAC	1m-2m
DGX H200	ConnectX-8 (QSFP-DD)	QSFP-DD 800G Passive DAC	1m-2m
HGX H100 (8-GPU)	Quantum-2 InfiniBand	QSFP-DD 800G or OSFP 800G	0.5m-3m
DGX B200	ConnectX-8 / CX9	OSFP 800G (check BOM)	1m-3m
Nvidia Spectrum-4	QSFP-DD switch port	QSFP-DD 800G Passive DAC	1m-3m

Passive vs Active DAC: Which to Choose?

Passive DAC (no electronics in the transceiver head): Best for distances up to 3m. Lower cost, lower power, no signal regeneration. Recommended for within-rack connections in DGX systems.

Active DAC: Contains a signal amplifier in the transceiver. Supports up to 5m with better signal integrity. Higher cost (~30-40% premium). Choose when passive signals fail link training.

Sourcing 800G DAC Cables: RFQ Checklist

Before sending a purchase order or RFQ to a supplier, confirm these 7 parameters:

Form factor: QSFP-DD or OSFP (check your switch datasheet)
Speed: 800G total, not 400G (common confusion with older inventory)
Length: Measure rack-to-rack or server-to-switch distance before ordering
Active or passive: Specify in the RFQ to avoid substitution
Platform coding: Request Nvidia/Mellanox-coded FW to avoid “Unsupported Transceiver” errors
MOQ and lead time: Standard orders ship in 2-3 weeks; urgent orders in 5-7 business days
Warranty: Minimum 2 years; confirm RMA process before ordering bulk

FAQ

Q: Will a generic 800G DAC cable work in a Nvidia DGX system?

A: Yes, provided the transceiver firmware is coded for Nvidia/Mellanox. Non-coded cables may show “Unsupported Transceiver” warnings in mlxlink or cause link training failures. Always specify “Mellanox-compatible” coding when ordering.

Q: What is the price difference between 800G DAC and 800G AOC for short reaches?

A: For 1-3m links, passive 800G DAC is typically 40-60% cheaper than AOC and performs identically. AOC is preferred for reaches over 3m or where cable weight/flexibility matters in dense racks.

Q: Can I mix QSFP-DD and OSFP ports with a breakout DAC?

A: Yes. An OSFP-to-QSFP-DD breakout DAC is available and commonly used when connecting Nvidia Quantum-2 switches (OSFP) to compute nodes with QSFP-DD ports. Confirm the breakout ratio (1x800G to 2x400G or 4x200G).

Q: What lead time should I plan for 800G DAC cables from a China OEM factory?

A: Standard production run is 10-15 business days for quantities under 500 units. For 500+ units with custom coding, plan 20-25 business days. Air freight to US/EU adds 5-7 days.

ABPTEL supplies 800G QSFP-DD and OSFP DAC cables factory-direct, with Nvidia/Mellanox, Arista, and Cisco compatibility coding available. Request a quote and receive a datasheet and sample pricing within 24 hours.

Talk to ABPTEL

Looking for the right optical hardware for your AI data center, GPU cluster, or FTTA project? ABPTEL ships from Shenzhen with OEM/ODM support, fast lead times, and engineering-level pre-sales advice.