Side-by-side specifications of the Synology DS1618+ and DS1621+, from official datasheets. Differences are highlighted.
| DS1618+ | DS1621+ | |
| CPU | Intel Atom C3538 | AMD Ryzen V1500B, 2.2 GHz |
| Cores / threads | 4 cores / 4 threads | 4 cores / 8 threads |
| RAM (base) | 4 GB DDR4 non-ECC SODIMM | 4 GB DDR4 ECC SODIMM |
| RAM (max) | 32 GB | 32 GB (16 GB x 2) |
| Drive bays | 6 | 6 |
| Expandable to | 10 (with 2× DX517) | 16 total with 2 DX517 units |
| M.2 slots | 2 (via optional adapter card) | 2 x M.2 2280 NVMe |
| Network | 4× 1GbE RJ-45 | 4 x 1GbE RJ-45 |
| 10GbE | optional | optional |
| Max raw capacity | 192 TB raw (with 2× DX517) | 256 TB raw with 2 DX517 units |
| Hot-swap | yes | yes |
| Form factor | Tower | desktop |
| Released | 2018 | 2020 |
| Power consumption | 56.86 W / 25.76 W | 51.22 W / 25.27 W |
| DSM at launch | — | — |
Pick the DS1621+ unless you’re getting the DS1618+ at a much better price: the 1621+ has a faster Ryzen CPU, a higher RAM ceiling (up to 32 GB vs 8 GB), and a better long-term platform. Both are 6-bay units with 2x expansion support and built-in 10GbE upgrade via PCIe, but only the DS1621+ supports M.2 NVMe SSD caching.