CX4

CX4 is a designation used in computer networking and data storage to denote a four-lane high-speed interconnect. The best-known use is 10GBASE-CX4, a copper-based physical layer for 10 Gigabit Ethernet and related high-speed interconnects. The CX4 interface combines four differential pairs into a single connector to deliver 10 Gbps of aggregate bandwidth over short direct-attached copper cables.

In 10GBASE-CX4 implementations, each lane typically carries about 2.5 Gbps, for a total of 10 Gbps. The cables are quad-lane twinax copper cables terminated with a CX4 connector on each end. These short direct-attach cables were used to connect servers, switches, or storage controllers within data centers, offering low latency for close-range links. The CX4 approach provided a cost-effective option for early 10 Gigabit deployments when alternative copper or fiber options were less practical. It was widely supported in the mid-2000s by several vendors, notably Cisco, but has largely been supplanted by newer standards and cabling options such as 10GBASE-SR, 10GBASE-T, and QSFP/SFP+ copper solutions.

Beyond 10GBASE-CX4, the CX4 designation has appeared in other, less common contexts related to high-speed interconnects or product names. There is no single universal standard beyond 10GBASE-CX4 that defines a CX4 interface; in practice, CX4 should be understood in context to refer to the four-lane copper interconnect described above or to a vendor-specific implementation.