What is the difference between AX AH Al and EAX?

What is the difference between AX AH Al and EAX?

eax is the 32-bit, “int” size register. 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.

What is al and ah in assembly language?

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. These names refer to the same physical register. When referring to registers in assembly language, the names are not case-sensitive.

Is Al part of EAX?

So AX is composed of AH:AL halves, and is itself the low half of EAX. (The upper half of EAX isn’t directly accessible as a 16-bit register; you can shift or rotate EAX if you want to get at it.)

What does AL mean in assembly?

Answered 9 years ago. The %al referes to the low byte of the %ax register, %ah in the same way referes to the high byte of the %ax register. In 32-bit assembly you can access the different parts of a register with different operands. A register is 32-bits (4 bytes).

What is EAX register used for?

eax. eax is a 32-bit general-purpose register with two common uses: to store the return value of a function and as a special register for certain calculations. It is technically a volatile register, since the value isn’t preserved. Instead, its value is set to the return value of a function before a function returns.

What does test EAX EAX do?

eax contains the return value of strcmp. test is like bitwise and except it only sets the flags. Anding a value with itself gives the same value, so test eax, eax sets the flags based on whatever eax contains. ZF is set when the result of an operation is zero.

What is an EAX?

A. E. (Environmental Audio Extensions) Sound card functions that reproduce the reverberation effects heard in different environments. Developed by Creative Labs, EAX provides an extension to the Windows DirectSound and OpenAL programming interfaces.

What is EAX register?

What is EAX used for?

eax is a 32-bit general-purpose register with two common uses: to store the return value of a function and as a special register for certain calculations. It is technically a volatile register, since the value isn’t preserved. Instead, its value is set to the return value of a function before a function returns.

Is EAX a general register?

As the title says, general register are the one we use most of the time Most of the instructions perform on these registers. EAX,AX,AH,AL : Called the Accumulator register. It is used for I/O port access, arithmetic, interrupt calls, etc…

What does Imul do in assembly?

Description. The single-operand form of imul executes a signed multiply of a byte, word, or long by the contents of the AL, AX, or EAX register and stores the product in the AX, DX:AX or EDX:EAX register respectively.

What does JLE do in assembly?

The jle instruction is a conditional jump that follows a test. It performs a signed comparison jump after a cmp if the destination operand is less than or equal to the source operand.

What is the difference between ah ah and al in Ax?

AH is the 8 high bits of AX (i.e. the bits 8-15 of EAX) and AL is the least significant byte (bits 0-7) of EAX as well as AX.

What is the difference between Ax and EAX?

83 No, that’s not quite right. EAX is the full 32-bit value AX is the lower 16-bits AL is the lower 8 bits AH is the bits 8 through 15 (zero-based) So AX is composed of AH:AL halves, and is itself the low half of EAX.

Is EAX 16 bit or 64 bit?

(The upper half of EAX isn’t directly accessible as a 16-bit register; you can shift or rotate EAX if you want to get at it.) For completeness, in addition to the above, which was based on a 32-bit CPU, 64-bit Intel/AMD CPUs have

Why does writing to Ax/EAX/Rax leave other bytes unmodified?

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. (In 32 or 64-bit code, prefer a movzx eax, byte [mem]or movzx eax, word [mem]load if you don’t specifically want this merging: Why doesn’t GCC use partial registers?