These topics contain information about assembler programming and the ISA for x86 processors up to the Intel 486.
For an overview of the CPU registers, refer to the Intel 8086 Family Architecture topic.
In the instruction topics, you will find clock counts for each CPU. The Instruction Clock Cycle Calculation topic describes the calculation in more detail.
If you are using MASM, you may find useful to check the MASM Command Line Options and the MASM Directives topics.
The Memory Model Programming & Segment Information topic describes the memory models supported by most MS-DOS assemblers.
Finally, for information on the flags register and the machine status word (286+ only), check the FLAGS and MSW topics respectively.
| AAA | Ascii Adjust for Addition |
| AAD | Ascii Adjust for Division |
| AAM | Ascii Adjust for Multiplication |
| AAS | Ascii Adjust for Subtraction |
| ADC | Add With Carry |
| ADD | Arithmetic Addition |
| AND | Logical And |
| ARPL | Adjusted Requested Privilege Level of Selector |
| BOUND | Array Index Bound Check (80188+) |
| BSF | Bit Scan Forward (386+ only) |
| BSR | Bit Scan Reverse (386+ only) |
| BSWAP | Byte Swap (486+ only) |
| BT | Bit Test (386+ only) |
| BTC | Bit Test with Compliment (386+ only) |
| BTR | Bit Test with Reset (386+ only) |
| BTS | Bit Test and Set (386+ only) |
| CALL | Procedure Call |
| CBW | Convert Byte to Word |
| CDQ | Convert Double to Quad (386+ only) |
| CLC | Clear Carry |
| CLD | Clear Direction Flag |
| CLI | Clear Interrupt Flag (disable) |
| CLTS | Clear Task Switched Flag (286+ privileged) |
| CMC | Complement Carry Flag |
| CMP | Compare |
| CMPS | Compare String (Byte, Word or Doubleword) |
| CMPXCHG | Compare and Exchange |
| CWD | Convert Word to Doubleword |
| CWDE | Convert Word to Extended Doubleword (386+ only) |
| DAA | Decimal Adjust for Addition |
| DAS | Decimal Adjust for Subtraction |
| DEC | Decrement |
| DIV | Divide |
| ENTER | Make Stack Frame (80188+) |
| ESC | Escape |
| HLT | Halt CPU |
| IDIV | Signed Integer Division |
| IMUL | Signed Multiply |
| IN | Input Byte or Word From Port |
| INC | Increment |
| INS | Input String from Port (80188+) |
| INT | Interrupt |
| INTO | Interrupt on Overflow |
| INVD | Invalidate Cache (486+ only) |
| INVLPG | Invalidate Translation Look-Aside Buffer Entry (486+ only) |
| IRET/IRETD | Interrupt Return |
Check the Jump Instructions Table topic for a summary of the various jump instructions.
| JA/JNBE | Jump Above / Jump Not Below or Equal |
| JAE/JNB | Jump Above or Equal / Jump on Not Below |
| JB/JNAE | Jump Below / Jump Not Above or Equal |
| JBE/JNA | Jump Below or Equal / Jump Not Above |
| JC | Jump on Carry |
| JCXZ/JECXZ | Jump if Register (E)CX is Zero |
| JE/JZ | Jump Equal / Jump Zero |
| JG/JNLE | Jump Greater / Jump Not Less or Equal |
| JGE/JNL | Jump Greater or Equal / Jump Not Less |
| JL/JNGE | Jump Less / Jump Not Greater or Equal |
| JLE/JNG | Jump Less or Equal / Jump Not Greater |
| JMP | Unconditional Jump |
| JNC | Jump Not Carry |
| JNE/JNZ | Jump Not Equal / Jump Not Zero |
| JNO | Jump Not Overflow |
| JNS | Jump Not Signed |
| JNP/JPO | Jump Not Parity / Jump Parity Odd |
| JO | Jump on Overflow |
| JP/JPE | Jump on Parity / Jump on Parity Even |
| JS | Jump Signed |
| LAHF | Load Register AH From Flags |
| LAR | Load Access Rights (286+ protected) |
| LDS | Load Pointer Using DS |
| LEA | Load Effective Address |
| LEAVE | Restore Stack for Procedure Exit (80188+) |
| LES | Load Pointer Using ES |
| LFS | Load Pointer Using FS (386+ only) |
| LGDT | Load Global Descriptor Table (286+ privileged) |
| LIDT | Load Interrupt Descriptor Table (286+ privileged) |
| LGS | Load Pointer Using GS (386+ only) |
| LLDT | Load Local Descriptor Table (286+ privileged) |
| LMSW | Load Machine Status Word (286+ privileged) |
| LOCK | Lock Bus |
| LODS | Load String (Byte, Word or Double) |
| LOOP | Decrement CX and Loop if CX Not Zero |
| LOOPE/LOOPZ | Loop While Equal / Loop While Zero |
| LOOPNZ/LOOPNE | Loop While Not Zero / Loop While Not Equal |
| LSL | Load Segment limit (286+ protected) |
| LSS | Load Pointer Using SS (386+ only) |
| LTR | Load Task Register (286+ privileged) |
| MOV | Move Byte or Word |
| MOVS | Move String (Byte or Word) |
| MOVSX | Move with Sign Extend (386+ only) |
| MOVZX | Move with Zero Extend (386+ only) |
| MUL | Unsigned Multiply |
| NEG | Two's Complement Negation |
| NOP | No Operation (90h) |
| NOT | One's Compliment Negation (Logical NOT) |
| OR | Inclusive Logical OR |
| OUT | Output Data to Port |
| OUTS | Output String to Port (80188+ only) |
| POP | Pop Word off Stack |
| POPA/POPAD | Pop All Registers onto Stack (80188+ only) |
| POPF/POPFD | Pop Flags off Stack |
| PUSH | Push Word onto Stack |
| PUSHA/PUSHAD | Push All Registers onto Stack (80188+ only) |
| PUSHF/PUSHFD | Push Flags onto Stack |
| RCL | Rotate Through Carry Left |
| RCR | Rotate Through Carry Right |
| REP | Repeat String Operation |
| REPE/REPZ | Repeat Equal / Repeat Zero |
| REPNE/REPNZ | Repeat Not Equal / Repeat Not Zero |
| RET/RETF | Return From Procedure |
| ROL | Rotate Left |
| ROR | Rotate Right |
| SAHF | Store AH Register into FLAGS |
| SAL/SHL | Shift Arithmetic Left / Shift Logical Left |
| SAR | Shift Arithmetic Right |
| SBB | Subtract with Borrow |
| SCAS | Scan String (Byte, Word or Doubleword) |
| SETAE/SETNB | Set if Above or Equal / Set if Not Below |
| SETB/SETNAE | Set if Below / Set if Not Above or Equal |
| SETBE/SETNA | Set if Below or Equal / Set if Not Above |
| SETE/SETZ | Set if Equal / Set if Zero (386+ only) |
| SETNE/SETNZ | Set if Not Equal / Set if Not Zero (386+ only) |
| SETL/SETNGE | Set if Less / Set if Not Greater or Equal |
| SETGE/SETNL | Set if Greater or Equal / Set if Not Less |
| SETLE/SETNG | Set if Less or Equal / Set if Not greater or Equal |
| SETG/SETNLE | Set if Greater / Set if Not Less or Equal |
| SETS | Set if Signed (386+ only) |
| SETNS | Set if Not Signed (386+ only) |
| SETC | Set if Carry (386+ only) |
| SETNC | Set if Not Carry (386+ only) |
| SETO | Set if Overflow (386+ only) |
| SETNO | Set if Not Overflow (386+ only) |
| SETP/SETPE | Set if Parity / Set if Parity Even (386+ only) |
| SETNP/SETPO | Set if No Parity / Set if Parity Odd (386+ only) |
| SGDT | Store Global Descriptor Table (286+ privileged) |
| SIDT | Store Interrupt Descriptor Table (286+ privileged) |
| SHR | Shift Logical Right |
| SHLD/SHRD | Double Precision Shift (386+ only) |
| SLDT | Store Local Descriptor Table (286+ privileged) |
| SMSW | Store Machine Status Word (286+ privileged) |
| STC | Set Carry |
| STD | Set Direction Flag |
| STI | Set Interrupt Flag (Enable Interrupts) |
| STOS | Store String (Byte, Word or Doubleword) |
| STR | Store Task Register (286+ privileged) |
| SUB | Subtract |
| TEST | Test For Bit Pattern |
| VERR | Verify Read (286+ protected) |
| VERW | Verify Write (286+ protected) |
| WAIT/FWAIT | Event Wait |
| WBINVD | Write-Back and Invalidate Cache |
| XCHG | Exchange |
| XLAT/XLATB | Translate |
| XOR | Exclusive OR |