I can just tell you that stall protection systems(SPS) have been installed in jets for decades and per this particular article it seems the latest concern is with the SPS.
SPS is more of a mechanical implementation of the processing of sensor data. You literally get physical feedback from the stick shaker on an impending stall and if the aircraft gets close enough to a stall the system will physically push the stick forward to break the stall.
MCAS works in conjunction with the pitch trim system. It uses the AOA sensor data to make adjustments to pitch trim which will result in a change to the angle of attack of the aircraft. This system works behind any feedback from or to the pilots. It's similar to fly-by-wire technology that almost all (or all) Airbus transport category aircraft have and some Boeing (but not the 737). Evidently Boeing offered some sort of optional software package that compared the data from both AOA sensors rather than having them operate independently as is the case with most jets that have SPS. How that works exactly, I don't know.
In both of these cases these systems may be disabled by the pilots.
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