1~2 and 3. On CCDs, the amplifier is effectively in the corner
of the sensor, but on CMOS, there is an amplifier built into
each photosite, dispersed throughout the sensor. See here. As
mentioned in one thing I recently discovered, most DSLRs have an
amplifier before the ADC (Analog-to-Digital Conversion). They
tend to max at 800 or 1600 ISO and are all digital
amplifications afterward. The following paragraphs assume a
camera that maxes out its analog amplification at 1600:
Unfortunately, the 12 or 14 bit RAW files prevent you from doing
what you describe. The digital amplification takes place before
the RAW files are stored. There is a maximum value that can be
stored, so when you shoot 4-stops overexposed, even though the
ADC is not saturated, the RAW file will probably be clipped.
However, the technique that overexposes just as much as to not
clip highlights is effective at reducing noise, and known as
ETTR (Expose To The Right). Yes, due to the analog
amplification, RAW files at higher ISO do contain mor