What is SQL Server buffer pool extension and how does it improve memory management?

Buffer Pool Extension uses SSD storage as an extension of memory for caching data pages.

Buffer Pool Extension (BPE) allows SQL Server to extend memory buffer pool onto fast SSD storage. It reduces physical disk IO by caching cold pages on SSD instead of disk. It is not a replacement for RAM but a hybrid tiered caching mechanism. SQL Server still prefers RAM first, then BPE, then disk. It is especially useful in memory-constrained environments with fast NVMe storage.