Because the controller and flash are on the same physical device in a very small amount of space, at least somewhat thermally coupled, not just by the PCB, but

Because the controller and flash are on the same physical device in a very small amount of space, at least somewhat thermally coupled, not just by the PCB, but by "heat spreaders" often sold with the drive or part of the motherboard. Google around and you'll see lots of thermal camera images of M2 drives. As the article points out, these drives consume up to ~10W under load. That's actually a lot of power for something with very, very little thermal mass - around 10 grams, and a heat capacity of around 400J/KgC is common for PCBs and chips. 0.4J/gC means that for just one second under full load, if the heat is generated evenly across the entire device, it will heat up 2.5 degrees C. Assuming no cooling, that's 24 seconds until it hits is thermal throttling point. From the article: > The amount of activity taking place on the gumstick-sized M.2 form factor means higher temps not only for the storage controller, but for the NAND flash itself. > NAND, Tanguy explains, is happiest within a relatively narrow temperature band. "NAND flash actually likes to be 'hot' in that 60° to 70° [celcius] range in order to program a cell because when it's that hot, those electrons can move a little bit easier," he explained. > Go a little too hot — say 80°C — and things become problematic, however. At these temps, you risk the SSD's built-in safety mechanisms forcibly powering down the system to prevent damage. However, before this happens users are likely to see the performance of their drives plummet, as the SSD's controller throttles itself to prevent data loss. FYI, Tanguy according to his linkedin is the principle product engineer for Micron.