CXL 4.0 doubles bandwidth, introduces bundled ports for data centres
The CXL Consortium has released the Compute Express Link 4.0 specification, responding to increasing demands on data centres by doubling available bandwidth and expanding features for system reliability and scalability.
Bandwidth increase
The CXL 4.0 specification raises the available transfer speed from 64GTs to 128GTs. This enhancement allows faster movement of data between devices connected with CXL, supporting workloads that demand low latency and high throughput. The update maintains the 256B Flit format introduced in previous versions, helping ensure performance consistency across different CXL generations.
Bundled ports
A new feature introduced with CXL 4.0 is support for bundled ports, which enable multiple ports on a device to be combined for higher aggregate bandwidth. The specification also supports native x2 width, allowing increased fan-out and the use of up to four retimers, which can extend the reach of CXL channels across platforms. The ability to combine device ports between host systems and accelerators is designed to provide additional flexibility for system architects.
Memory enhancements
The specification delivers improvements to memory reliability, availability, and serviceability (RAS). The enhanced RAS features are intended to increase error visibility and maintenance efficiency while maintaining compatibility with previous versions of the specification. The Consortium stated that backward compatibility is retained with CXL 3.x, 2.0, 1.1, and 1.0, enabling broader industry adoption and smoother transition for existing deployments.
Industry collaboration
CXL Consortium President and Treasurer, and Principal Engineer at NVIDIA, Derek Rohde, emphasised the collaborative nature of the new specification's development.
"The release of the CXL 4.0 specification sets a new milestone for advancing coherent memory connectivity, doubling the bandwidth over the previous generation with powerful new features. This release reflects our member companies' commitment to driving open standards that empower data center innovation, support compliance and interoperability, and enable the entire industry to scale for future usage models," said Derek Rohde, President and Treasurer, CXL Consortium.
