According to a video by Gamers Nexus, AMD's reference RX 7900 XTX features a unique ambient thermal sensor that allows the GPU to measure air-inlet temperatures coming directly into the cooler. We don't know why AMD added this sensor to its cards, but it has the potential to be very useful.
There are several benefits to having an ambient thermal sensor inside your GPU cooler. Gamers Nexus notes that one of the most significant advantages is to monitor ambient temperatures while the fans are off (0db mode), to keep PCB components on the card from overheating.
Gamers Nexus continues, saying this exact issue was a problem on EVGA's GTX 10 series graphics cards before the ICX coolers were introduced. The 0db mode of the cards accidentally caused some of the power delivery components to overheat and die prematurely. As a result, EVGA recalled those cards and eventually replaced them with ICX coolers featuring additional thermal sensors.
However, it's worth mentioning that this was a one-time ordeal, and almost every card on the market today has a zero RPM fan mode, with coolers designed to take advantage of that feature.
In the case of the 7900 XTX, AMD probably added this sensor as an added security measure, just in case some of the PCB components get too hot while the GPU core is still cool enough to keep the fans off. Once temps get too warm, the card can initiate a secondary fan curve to keep the PCB components cool while operating the fans at a very low RPM.
Hopefully, AMD will provide end-users access to this sensor inside the Adrenalin control panel (and 3rd party applications) since it could be helpful in several scenarios - not just for keeping the card cool. For example, the ambient sensor can also be used to measure the actual ambient temperature inside the entire system to monitor and troubleshoot high temperatures on other components and/or fault chassis fans.
Unfortunately, AMD neglected to share why it added this sensor to its reference cards, leaving us to speculate. But if we get an official comment from AMD, we’ll update you here on the details.
...Or something along those lines.
I suppose stuffing a sensor in there is the lazy work-around for not characterizing the HSF beyond making sure it can cope with max load under worst-case supported conditions.
I guess that's the best way to characterize that external sensor: overkill XD
Not that I may necessarily need it, having thermal sensor on MB, according to which there isn't any heat building up, with so far sufficient air flow. But at least getting the read-out would sure seem nice.