The Synology D4EC-2666-16G is a 16GB DDR4 ECC unbuffered UDIMM memory module engineered for high-performance RackStation and SA series NAS systems. Operating at 2666 MHz, this 288-pin module utilizes ECC technology to proactively detect and repair data corruption, maintaining system stability for mission-critical enterprise applications. As an official Synology upgrade, it is rigorously tested for seamless compatibility with models like the RS4021xs+, RS3621xs+, and SA3400D. This module is optimized for I/O-intensive workloads, including virtualization and 24/7 data management, ensuring robust performance and long-term reliability.