Side-by-side specifications of the Synology DS508 and DS509+, from official datasheets. Differences are highlighted.
| DS508 | DS509+ | |
| CPU | — | Intel Celeron |
| Cores / threads | — | — |
| RAM (base) | — | 512 MB |
| RAM (max) | — | 512 MB |
| Drive bays | 5 | 5 |
| Expandable to | — | 10 |
| M.2 slots | 0 | 0 |
| Network | 2x GbE | 2x Gigabit |
| 10GbE | no | no |
| Max raw capacity | 5x HDD | 30 TB |
| Hot-swap | yes | yes |
| Form factor | desktop | desktop |
| Released | 2008 | 2009 |
Pick the DS509+ if you want the stronger box: it has a faster CPU and a higher RAM ceiling, while the DS508 is the older, weaker option. Both are 5-bay units with no expansion, and neither has built-in 10GbE or M.2 support. For a home/SMB buyer, the DS509+ is the safer choice unless you’re only buying on price and basic storage needs.