CXL 4.0 Doubles Bandwidth And Stretches Memory Pooling To Multi-Rack Setups
Blocks & Files, Monday, November 24th, 2025
The fourth CXL memory sharing spec adds speed and extends distance for multi-rack systems. The Computer eXpress Link (CXL) specification defines how pools of memory can be connected across the PCIe bus.
There have been three generations. CXL 1 enabled x86 servers to access PCIe 5.0-linked memory in external devices like SmartNICs and DPUs. CXL 2 added memory pooling between servers and external devices, still with PCIe 5.0, while CXL 3 added switches and PCIe 6.0, so more servers and devices could share memory. Now we have CXL 4.0 which uses PCIe 7.0 to add speed and has additional features to increase memory pool span and bandwidth. The rising need for multi-rack AI servers is a target area for this.