Editing Motorola 68000 (section)

===Internal registers===
The [[Central processing unit|CPU]] has eight 32-bit general-purpose data [[processor register|registers]] (D0-D7), and eight address registers (A0-A7). The last address register is the [[stack (data structure)|stack pointer]], and assemblers accept the label SP as equivalent to A7. This was a good number of registers at the time in many ways. It was small enough to allow the 68000 to respond quickly to [[interrupt]]s (even in the worst case where all 8 data registers D0–D7 and 7 address registers A0–A6 needed to be saved, 15 registers in total), and yet large enough to make most calculations fast, because they could be done entirely within the processor without keeping any partial results in memory. (Note that an exception routine in supervisor mode can also save the user stack pointer A7, which would total 8 address registers. However, the dual stack pointer (A7 and supervisor-mode A7') design of the 68000 makes this normally unnecessary, except when a task switch is performed in a multitasking system.)

Having the two types of registers allows one 32-bit address and one 16-bit data calculation to take place at the same time. This results in reduced instruction execution time as addresses and data can be processed in parallel.<ref name="Starnes" />