This 16GB RAM is 100% compatible with Fujitsu D3646-S. Information regarding memory configuration: The following technical specifications should be considered in advance: A higher memory clock of the memory module automatically adjusts to the clock specified by the system. This can especially be the case with larger capacities. Non-ECC or ECC (Error-Correction-Code) RAM can be installed in the device. Modules labeled ECC have error correction. Non-ECC memory modules cannot be mixed with ECC memory. If a memory upgrade is to be made with the existing RAM, it must be checked which memory technology (non-ECC / ECC) is present. If memory modules with higher clock rates than specified by the system are offered, the memory clock will automatically adjust to the system specifications.