This product is either discontinued or we cannot get that from suppliers.
Synology 4GB DDR3 RAM Module, 4 GB, DDR3 SODIMM, Unbuffered, Speed 1600 MHz, 1.5 V, 204-Pin, CAS Latency 11.
The Synology 4GB 204-Pin SODIMM DDR3 RAM Module improves the performance of your Synology NAS server by providing additional short-term memory. To use this RAM chip, your server must have a 204-pin SODIMM.