CXL Type 3 device (memory expander)
Beginner
A card full of extra memory that plugs into the fast PCIe wires instead of a memory slot.
Novice
A CXL device that holds memory and lets the CPU read and write it like normal memory. It adds capacity and bandwidth without adding memory channels to the CPU, at the cost of some extra delay.
Expert
Implements CXL.io and CXL.mem only. Appears to software as a CPU-less NUMA node. Load latency is roughly a remote-socket access or more, depending on the controller; useful for capacity tiers and pooling.
Explained in Board and server (Systems).
See also: CXL (Compute Express Link), NUMA (non-uniform memory access).