The Synology D4ES01-8G is an 8 GB memory module for adding memory to compatible Synology NAS systems.
It uses DDR4 ECC unbuffered SODIMM memory. This combination identifies the module’s memory type and form, while ECC provides error-correcting capability in supported systems.
Synology lists the RS1221RP+, RS1221+, DS1821+, DS1621xs+, and DS1621+ among the compatible models. The module is intended for these NAS systems as an additional memory component.