Abstract: A digital data encoding and decoding method and system is disclosed, with particular reference to magnetic records, in which bits are encoded in groups. Three out of four, two-bit combinations are encoded respectively by three patterns of transition placements under the rule that the two-bit group frame be divisible in only three sections having width of the read resolution R and the minimum spacing M between transitions is twice that value. The fourth bit combination is encoded under utilization of altogether four bits, using pattern combinations that extend over six sections R under the same constraint as to minimum spacing. Under otherwise similar conditions, the package density can be increased by 33% as compared with tri-period codes, and more than doubled as compared with frequency doubling or Manchester.