RTL2832U: 7 or 8-bits ?

quick question concerning the RTL2832U ADC: is it 7 bit (as stated on the Realtek web page in the cryptic "7-bit ADC for RF signals level measurement" or 8-bit as stated on the osmosdr web page ? or is it 7 bit + sign = 8 bits ? I am computing the gain from oversampling wrt a sound card, and not that it matters much but I'd rather have the figures right. Thanks, JM