Industry Expert Blogs

CXL™ 3.0 Turns Up Scalability to 11

- Rambus, Inc.
Aug 02, 2022

The CXL™ Consortium (of which Rambus is a member) has now released the 3.0 specification of the Compute Express Link™ (CXL) standard. CXL 3.0 introduces compelling new features that promise to increase data center performance, scalability and TCO. CXL has evolved rapidly from its introduction in 2019. The 1.0/1.1 specification enabled prototyping of CXL solutions. With 2.0 and the introduction of memory pooling, CXL reached the deployment phase. Now with CXL 3.0, we have capabilities that will power the scaling phase.

So, what's new in CXL 3.0? Well, first up there's a step function increase in data rate. CXL 1.x and 2.0 use the PCI Express® (PCIe®) 5.0 electricals for their physical layer: NRZ signaling at 32 Gigatransfers per second (GT/s). CXL 3.0 keeps that same philosophy of building on broadly adopted PCIe technology and extends it to the latest 6.0 version of the PCIe standard released earlier this year. That boosts CXL 3.0 data rates to 64 GT/s using PAM4 signaling.

A second big addition with CXL 3.0 is multi-tiered switching which enables the implementation of switch fabrics. CXL 2.0 allowed for a single layer of switching. CXL 2.0 switches can connect to upstream hosts and downstream devices, but not other switches, and the scale is limited to the available ports on a switch. With CXL 3.0, switch fabrics are enabled, where switches can connect to other switches, vastly increasing the scaling possibilities.

Among additional features, CXL 3.0 introduces peer-to-peer direct memory access and enhancements to memory pooling where multiple hosts can coherently share a memory space on a CXL 3.0 device. These features enable new use models and increased flexibility in data center architectures. Taken together with 64 GT/s signaling and fabric switching, CXL 3.0 puts us on the road for composable server systems which optimize performance and TCO.

CXL is a-once-in-a-decade technological force that will transform data center architectures. Supported by a who's who of industry players including hyperscalers, system OEMs, platform and module makers, chip makers and IP providers, its rapid development is a reflection of the tremendous value it can deliver. Rambus is proud to be a member of the CXL Consortium and to provide chip and IP solutions that will shape the data center of the future.

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