When sourcing DDR RAM, the most critical factor is generational compatibility (DDR3, DDR4, or DDR5), as these are not backward compatible due to different pin counts and voltage requirements. You must verify the frequency (MHz) and latency (CL) to ensure they match the target motherboard's specifications. For industrial or server applications, specify whether you require ECC (Error Correction Code) or Non-ECC modules, and distinguish between UDIMM (Desktop), SODIMM (Laptop), and RDIMM (Server) form factors.