Side-by-side specifications of the Synology DS509+ and DS620slim, from official datasheets. Differences are highlighted.
| DS509+ | DS620slim | |
| CPU | Intel Celeron | Intel Celeron J3355 |
| Cores / threads | — | 2/2 |
| RAM (base) | 512 MB | 2 GB |
| RAM (max) | 512 MB | 6 GB |
| Drive bays | 5 | 6 |
| Expandable to | 10 | 0 |
| M.2 slots | 0 | 0 |
| Network | 2x Gigabit | 2x 1GbE |
| 10GbE | no | no |
| Max raw capacity | 30 TB | 108 TB |
| Hot-swap | yes | yes |
| Form factor | desktop | mini 6-bay NAS |
| Released | 2009 | 2018 |
Choose the DS620slim if you want a newer platform with a newer Intel Celeron CPU, more RAM headroom, and 6 bays instead of 5; it also supports M.2 SSD slots, while the DS509+ does not. Neither model has built-in 10GbE, and the DS509+ is older and less capable on CPU/RAM expansion.