Samsung MEX

Samsung's MEX is the SATA controller used in the 840 EVO from 2013. It is a 3-core ARM Cortex-R4 design and the first Samsung consumer SSD controller to support TLC NAND at scale, which let the 840 EVO reach 1TB at a competitive price point.

The MEX controller implements Samsung's TurboWrite technology, which designates a portion of TLC NAND as an SLC write buffer for burst performance. Outside the buffer, sustained write speeds drop considerably – a characteristic of TLC designs of this era. A separate firmware issue later emerged where read performance on 840 EVO drives degraded over time on infrequently-accessed data, addressed by Samsung via firmware updates in 2014–2015.