This content has not been validated; it was AI-generated following the x86-64 ISA Documentation generation process to maintain high quality. However, as no human has verified this data, errors may exist. If the accuracy of this data is critical, please consult the Intel SDM. The model used to generate this is gemma4:31b

MOVSB

Copies a byte from the memory location pointed to by RSI to the memory location pointed to by RDI, then increments or decrements RSI and RDI by 1 based on the Direction Flag (DF).

The table below covers what the source and destinations can be.

DO NOT support LOCK

The instruction SHALL be used in conjunction with the DF flag; if DF=0, RSI and RDI are incremented, if DF=1, they are decremented. It is available in 64-bit mode and compatibility mode.

To avoid unintended memory corruption or infinite loops when using the REP prefix, the user MUST ensure that the RCX register is initialized with the correct count and that the memory regions pointed to by RSI and RDI do not overlap in a manner that violates the intended copy logic.