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

INSB

Reads a byte from the location pointed to by the ESI or RSI register (or EDI/RDI if the direction flag DF is set), stores it into the AL or R8B register, and then increments or decrements the index register by 1.

The table after the description covers what the source and destinations can be.

DO NOT support LOCK

The instruction is only available when the processor is in 32-bit mode or 64-bit mode. In 64-bit mode, the index register used is RSI or RDI unless a 32-bit operand size prefix is used, in which case ESI or EDI is utilized.

The behavior of the index register modification is dependent on the Direction Flag (DF) in the RFLAGS register: if DF=0, the index register is incremented; if DF=1, the index register is decremented. Failure to correctly initialize the DF flag before execution MAY result in memory access violations or incorrect data retrieval.