Writing AL, AH, or AX leaves other bytes unmodified in the full AX/EAX/RAX, for historical reasons. i.e. it has to merge a new AL into the full RAX, for example.

Some of these data registers have specific use in arithmetical operations. AX is the primary accumulator; it is used in input/output and most arithmetic instructions. For example, in multiplication operation, one operand is stored in EAX or AX or …

For example, the least significant 2 bytes of EAX can be treated as a 16-bit register called AX. The least significant byte of AX can be used as a single 8-bit register called AL, while the most significant byte of AX can be used as a single 8-bit register called AH.

As it is widely advertised, modern x86_64 processors have 64-bit registers that can be used in backward-compatible fashion as 32-bit registers, 16-bit registers and even 8-bit registers, for example: ================ rax (64 bits) ======== eax (32 bits) ==== ax (16 bits) == ah (8 bits) == al (8 bits)

We can see that the RAX register contains a 32-bit EAX sub-register, a 16-bit AX sub-register, and two 8-bit sub-registers AH and AL. When you manipulate the contents of one of these sub-registers, it affects the corresponding portion of the larger register.

Oct 31, 2021 · The least significant byte of AX can be used as a single 8-bit register called AL, while the most significant byte of AX can be used as a single 8-bit register called AH.

ax is the 16-bit, "short" size register. It was added in 1979 with the 8086 CPU, but is used in DOS or BIOS code to this day. al and ah are the 8-bit, "char" size registers. al is the low 8 bits, ah is the high 8 bits. They're pretty similar to the old 8-bit registers of the 8008 back in 1972.

May 15, 2016 · I'm having trouble understanding registers in x86 Assembly, I know that EAX is the full 32 bits, AX is the lower 16 bits, and then AH and AL the higher and lower 8 bits of AX, But I'm doing a question. If AL=10 and AH=10 what is the value in AX?

rs. The lower 16 bits of the EAX register corresponds to the AX register, and similarly for the other regi ers. This means that AH corresponds to the second low-order byte of EAX, and that AL corresponds to the low-order b

Used in Binary-Coded Decimal (BCD) arithmetic. # eax - ebx je ... L1 # ebx != eax L1: ... ZF (Zero Flag): 1 if result is zero. 0 otherwise. SF (Sign Flag): Set equal to the most-significant bit of the result. Sign bit for a signed integer. CF (Carry Flag): Overflow condition for unsigned arithmetic.