CXL Consortium Compute Express Link 2.0 specification

The CXL 2.0 specification adds support for switching for fan-out to connect to more devices; memory pooling for increased memory utilisation efficiency and providing memory capacity on demand; and support for persistent memory – all while preserving industry investments by supporting full backwards compatibility with CXL 1.1 and 1.0.

“Datacenter architectures continue to evolve rapidly to support the growing demands of emerging workloads for Artificial Intelligence and Machine Learning, with CXL technology keeping pace to meet the performance and latency demands,” said Barry McAuliffe, President, CXL Consortium. “Designed with breakthrough performance and easy adoption as guiding principles, the CXL 2.0 specification is a significant achievement from our dedicated technical work group members.”  

Highlights of the CXL 2.0 specification:

• Adds support for switching to enable device fan-out, memory scaling, expansion and the migration of resources.
• Includes memory pooling support to maximise memory utilisation, limiting or eliminating the need to overprovision memory.
• Introduces standardised fabric manager specification for inventory and resource allocation to enable easier adoption and management of CXL-based switch and fabric solutions.
• Provides standardised management of the persistent memory interface and enables simultaneous operation alongside DDR, freeing up DDR for other uses.
• Introduces managed hot-plug support to take a CXL device online or offline from the system.
• Adds link-level Integrity and Data Encryption (CXL IDE) to provide confidentiality, integrity and replay protection for data transiting the CXL link.
• Supports a wide variety of industry interconnect form factors and standardised management interfaces to ease implementation.
• Includes Compliance and Interoperability specifications and in-system testing to enable a robust and interoperable multi-vendor ecosystem. 

“The CXL Consortium has moved with breathtaking speed to deliver its second generation CXL 2.0 spec, even before products incorporating the first generation CXL 1.0 and 1.1 specs have reached the market,” said Nathan Brookwood, Research Fellow at Insight 64.

“The new 2.0 features, including switching, memory pooling and persistent memory support pave the way for fully disaggregated systems in which pools of accelerators, DRAM and persistent memory storage can be dynamically connected to any one of 16 host servers to meet application demands. These features will enable system designers to invent entirely new types of systems that architects could only dream about just a few years ago.”