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 exampl Rax is the full 64-bit value, with eax and its sub-components mapped to the lower 32 bits. The upper half of 64-bit registers is only accessible in 64-bit mode, unlike 32-bit registers which can be used in …