XMP is an SPD extension. XMP, or eXtreme Memory Profiles, are higher-performance specs jammed into the leftover space in the EEPROM. These are conceptually the same thing as the JEDEC profiles, but they’re optimized by the memory manufacturer. XMP contains settings that the memory manufacturer says will probably work, but may not be supported depending on the quality of the CPU IMC or SOC and other components. For enthusiast RAM, the advertised speeds are usually only attainable by applying XMP.