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 |
| Cores / threads | 4-core | 4 |
| RAM (base) | 4 GB DDR4 | 4 GB |
| RAM (max) | 32 GB | 32 GB |
| Drive bays | 6 | 6 |
| Expandable to | 12 | 16 |
| M.2 slots | 2 | 2 |
| Network | 4 x 1GbE | 4x 1GbE RJ-45 |
| 10GbE | optional | optional |
| Max raw capacity | 72 TB | 256 TB |
| Hot-swap | yes | yes |
| Form factor | desktop | desktop |
| Released | 2018 | 2020 |
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.