While the previous products QNAP offered basically kept increasing storage capacity by adding more drive bays, the TS-509 Pro actually offers a serious hardware upgrade.
Upgrading the CPU to a 1.6 GHz Celeron backed by 1 GB of DDR2 RAM should prove to increase performance, as previous models were bottlenecked by the low-power but relatively slow ARM CPU.

Some of the features, as QNAP advertises them.
| Application: | 5×3.5″ SATA HD, up to 5 USB devices, 1x eSATA |
|---|---|
| Dimensions: | 261 x 188 x 261 mm (H x W x D) |
| Interface: | 2x Gigabit Ethernet |
| Power supply: | ATX 250W, Input: 100-264 Vac~, 46-63Hz, 5A |
| Supported filesystems: | FAT, FAT32, EXT3, NTFS (read only) |
| Hardware specifications: | CPU: Celeron 420 @ 1.6 GHz RAM: 1 GB DDR2 |
| Weight | 7Kg |