Side-by-side specifications of the Synology DS1520+ and DS1621+, from official datasheets. Differences are highlighted.
| DS1520+ | DS1621+ | |
| CPU | Intel Celeron J4125 | AMD Ryzen V1500B, 2.2 GHz |
| Cores / threads | 4 cores / 4 threads | 4 cores / 8 threads |
| RAM (base) | 8 GB DDR4 non-ECC | 4 GB DDR4 ECC SODIMM |
| RAM (max) | 8 GB | 32 GB (16 GB x 2) |
| Drive bays | 5 | 6 |
| Expandable to | 15 total (2 DX517) | 16 total with 2 DX517 units |
| M.2 slots | 2 NVMe M.2 2280 | 2 x M.2 2280 NVMe |
| Network | 4 x 1GbE RJ-45 | 4 x 1GbE RJ-45 |
| 10GbE | no | optional |
| Max raw capacity | 80 TB internal raw; 108 TB maximum single volume | 256 TB raw with 2 DX517 units |
| Hot-swap | yes | yes |
| Form factor | Desktop | desktop |
| Released | 2020 | 2020 |
| Power consumption | 52.06 W / 16.07 W | 51.22 W / 25.27 W |
| DSM at launch | 7.0 | — |