40GBASECR4

40GBASECR4 is a standard for high-speed Ethernet connectivity, specifically designed for short-reach applications within data centers. It operates at a data rate of 40 Gigabits per second. The "CR" in the designation stands for Copper Direct Attach Cable, indicating that it uses copper cabling for its physical medium. The "4" signifies that the link is comprised of four parallel lanes, each operating at 10 Gigabits per second, which are then aggregated to achieve the 40 Gbps total bandwidth.

This standard is commonly used for interconnections between servers, switches, and storage devices over distances typically up to 7 meters, though some specifications allow for slightly longer reaches. 40GBASECR4 utilizes QSFP+ (Quad Small Form-factor Pluggable Plus) transceivers, which are compact modules that house the optical or electrical components. The copper cables are usually twinaxial or quad-axial cables that feature integrated QSFP+ connectors on each end.

The primary advantages of 40GBASECR4 include its cost-effectiveness and low latency compared to fiber optic alternatives for short distances. It simplifies cabling by using a single cable assembly instead of multiple individual cables for lower speed Ethernet. This makes it a popular choice for top-of-rack (ToR) and end-of-row (EoR) deployments where high bandwidth is required over short, defined paths.