the only purpose the sensor has is to collecting photons
Disagree - it does more. The photon wells collect photons, there is a lot of additional circuitry on a sensor besides just the photon wells.
TrumpetPower is absolutely correct in his statement that, "ISO 50 and highlight tone priority are two special cases. The exact same analog signal amplification (i.e., none) is applied with all three exposures: ISO 50, ISO 100, and ISO 200 w/ HTP. If you use the same shutter speed and aperture, you'll get the exact same raw file in all three cases." (well, almost correct - the base ISO isn't exactly 100 for all sensors, so even at ISO 100, some gain may be applied - but it is the same gain in all three cases). He's also correct about ISO 50 being a linear 50% reduction, but incorrect about HTP being a linear doubling (HTP processing is application of a tone curve to boost the shadows and midtones but not the highlights).
HTP. it is a halving of infaling light= halving of the amount of charged electrons= go from 100 to 200 iso and make a head room, the analog signal is different = 100iso and 200 iso
Disagree. When you set ISO 200 with HTP, the camera is actually exposing at ISO 100, which is why ISO 100 cannot be set with HTP on, but (incorrectly) reporting ISO 200 in the metadata and setting the HTP flag. If you open an HTP RAW file in something like Rawnalyze, you'll see it's a stop underexposed - it's not halving the incoming light, it's reducing the analog gain applied to the same amount of light, by one stop.