The AX Series in x86 assembly language refers to the 16-bit AX register, a core component of CPU operations for data movement and arithmetic calculations. As a general-purpose register, AX (Accumulator) handles critical tasks like storing intermediate results, managing I/O operations, and facilitating memory addressing through variants like AH (high byte) and AL (low byte). For instance, MOV AX, 1200H loads the hexadecimal value 1200 into AX, while MOV AX, [BX] transfers data from memory addressed by BX to AX. Pro Tip: Use AX for division/multiplication operations—DIV and MUL instructions implicitly utilize AX for operand storage.
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What addressing modes involve the AX register?
AX participates in immediate, register, and memory addressing. For example, MOV AX, [BX+SI+1234H] uses base-index-displacement addressing to fetch data from DS:BX+SI+1234H. Pro Tip: Always verify segment registers (DS/SS) when calculating physical addresses—mismatched segments cause data corruption. Did you know that AX’s 16-bit structure allows efficient word-sized operations? For instance, MOV AX, [1200H] retrieves two bytes from memory at 21200H (assuming DS=2000H) into AX as 4C2AH.
How does AX interact with arithmetic operations?
AX serves as the default operand for MUL and DIV instructions. Multiplying 8-bit values (e.g., MUL BL) stores the 16-bit result in AX. Similarly, DIV CX divides DX:AX by CX, with the quotient in AX and remainder in DX. Pro Tip: Clear DX before 16-bit division to prevent overflow errors. Why is AX pivotal here? Its dual-byte structure (AH/AL) simplifies byte/word operations—ADD AL, 05H modifies only the lower byte without affecting AH.
| Operation | AX Role | Example |
|---|---|---|
| Multiplication | Stores result | MUL BL → AX=AL*BL |
| Division | Holds dividend | DIV CX → AX=(DX:AX)/CX |
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FAQs
No—AX is 16-bit. Use EAX (32-bit) or RAX (64-bit) in extended architectures.
Why does DIV require DX:AX?
For 32-bit dividends. DX holds high word, AX the low word before division.
Is AX preserved across function calls?
No—always save AX to stack if needed post-call, as INT 21H alters its value.
