MOVS? Command
This instruction gets a byte or a word from the data pointed to by DS:SI and copies it to the data pointed to by the ES:DI address. When the instruction is finished, SI and DI will be incremented or decremented accordingly with the status of the direction flag. So, if DS:SI pointed to a byte with the number 30, a "MOVSB" instruction would copy into the byte pointed to by ES:DI the number 30.