Specification: 2GB RAM | DDR2 | 200 Pin DIMM | SO DIMM | 800MHz PC2-6400S | 1.8 Volt The memory is 100% compatible with QNAP TS-559 Pro. The memory has been tested by us and approved for the device. Free support via our PHS memory hotline. 5 year warranty: If the memory module is defective within 5 years after purchase date or fails, you will receive an adequate RAM module free of charge after return. If the memory module is no longer available, we will refund the purchase price. The return address for warranty claims can be found at the top under the seller link "PHS-electronic GmbH". This warranty does not restrict your statutory warranty rights. The memory of the QNAP TS-559 Pro device can be adjusted to max. 2 GB.