Data registers are used for temporary scratch storage of data, as well as for data manipulations (arithmetic, logic, etc.). In some processors, all data registers act in the same manner, while in other processors different operations are performed are specific registers.

* MIX: one extension register; named X-register; five bytes plus sign; can be concatenated on the right hand side of the A-register (accumulator)
* Motorola 680x0, 68300: 8 longword (32 bit) data registers; named D0, D1, D2, D3, D4, D5, D6, and D7