The Synology D4EC-2666-16G is a memory module with a total capacity of 16 GB, specifically designed to enhance the performance of compatible Synology NAS servers, such as the RS4017xs+, RS3617xs+, and RS3617RPxs. This DDR4 SDRAM module, featuring a capacity per module of 16 GB, operates at a memory speed of 2666 MHz (PC4-21300) and utilizes a 288-pin DIMM form factor to fit securely into the server's memory slots. To ensure high data reliability and prevent system crashes, this unbuffered, single-rank memory features built-in Error Correcting Code (ECC), which detects and fixes internal data corruption. It operates at a power-efficient 1.2 V and is visually identified by its green PCB. For those using the RS4017xs+ model, you will need to have DSM 6.2.2-24922-6 or a newer version installed to ensure full compatibility with this hardware upgrade.