VARIABLES

Declaration of Variables

section .data
    num DB 1
    num2 DB 2

section .text
    global _start

_start:
    MOV bl,[num]
    MOV cl,[num2]

• Declared one-byte variable for num and num2, with initial values of 1 and 2 respectively;
• Loaded the values of the declared variables into the bl and cl registers, which represent the lower 8 bits of the bx and cx registers;

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Efficient Memory Usage

• x86 maximizes memory usage by storing bytes next to each other;
• Accessing a single byte from a memory slot, I will retrieve the entire 32-bit chunk it belongs to;
• Accessing these values directly can lead to unexpected results due to x86’s memory efficiency;

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Register Referencing

• Removing the e (ebx -> bx) prefix slices the register in 16 bits;
• Removing the e and x (ebx -> bl or bh) suffix references the lower or higher 8-bit parts;

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High vs. Low Bits

• By referencing the lower 8 bits of the registers, I ensure we’re working with the correct byte-sized data;
• Setting high bits (bh or ch) affects the interpretation of the entire register;
• High bits are interpreted differently due to their position in the binary representation;