In a Hamming code , each bit of data is covered by several parity bits . To start with , he developed a nomenclature to describe the system , including the number of data bits and error-correction bits in a block . For instance , parity includes a single bit for any data word , so assuming ASCII words with 7-bits , Hamming described this as an ( 8,7 ) code , with eight bits in total , of which 7 are data .