字符串是存储器中连续位置处可用的一系列数据字节或字。它被称为字节字符串或字符串。它们的内存始终按顺序分配。用于操纵字符串的指令称为字符串操纵指令。
下表显示了字符串操作指令列表：
| OPCODE | OPERAND | EXPLANATION | EXAMPLE |
|---|---|---|---|
| REP | instruction | repeat the given instruction till CX != 0 | REP MOVSB |
| REPE | instruction | repeat the given instruction while CX = 0 | REPE |
| REPZ | instruction | repeat the given instruction while ZF = 1 | REPZ |
| REPNE | instruction | repeat the given instruction while CX != 0 | REPNE |
| REPNZ | instruction | repeat the given instruction while ZF = 0 | REPNZ |
| MOVSB | none | moves contents of byte given by DS:SI into ES:DI | MOVSB |
| MOVSW | none | moves contents of word given by DS:SI into ES:DI | MOVSW |
| MOVD | none | moves contents of double word given by DS:SI into ES:DI | MOVD |
| LODSB | none | moves the byte at address DS:SI into AL; SI is incr/decr by 1 | LODSB |
| LODSW | none | moves the word at address DS: SI into AX; SI is incr/decr by 2 | LODSW |
| LODSD | none | moves the double word at address DS:SI into EAX; SI is incr/decr by 4 | LODSD |
| STOSB | none | moves contents of AL to byte address given by ES:DI; DI is incr/dec by 1 | STOSB |
| STOSW | none | moves the contents of AX to the word address given by ES:DI; DI is incr/decr by 2 | STOSW |
| STOSD | none | moves contents of EAX to the DOUBLE WORD address given by ES:DI; DI is incr/decr by 4 | STOSD |
| SCASB | none | compares byte at ES:DI with AL and sets flags according to result | SCASB |
| SCASW | none | compares word at ES:DI with AX and sets flags | SCASW |
| SCASD | none | compares double word at ES:DI with EAX and sets flags | SCASD |
| CMPSB | none | compares byte at ES:DI with byte at DS:SI and sets flags | CMPSB |
| CMPSW | none | compares word at ES:DI with word at DS:SI and sets flags | CMPSW |
| CMPSD | none | compares double word at ES:DI with double word at DS:SI and sets flags | CMPSD |