1. A multiprogramming method of a nonvolatile memory (NVM) device, the NVM device including a plurality of memory cells programmable in at least SET and RESET states, the method comprising: receiving input data bits from an external source; SET programming, according to the input data bits, a first sub-group of memory cells among the plurality of memory cells; SET programming, according to the input data bits, at least one second sub-group of memory cells among the plurality of memory cells, wherein the SET programming of the first sub-group is executed separately from the SET programming of the at least one second sub-group; RESET programming, according to the input data bits, the first sub-group of memory cells; RESET programming, according to the input data bits, the at least one second sub-group of memory cells, wherein the RESET programming of the first sub-group is executed separately from the RESET programming of the at least one second sub-group.