Direction flag

The direction flag is a flag that controls the "left-to-right" or "right-to-left" direction of string processing, stored in the FLAGS register on all x86-compatible CPUs. It is bit number 10.
This flag is used to determine the direction ('forward' or 'backward') in which several bytes of data will be copied from one place in the memory, to another. The direction is important mainly when the original data position in memory and the target data position overlap.