The idiv instruction divides the contents of the 64 bit integer EDX:EAX ( constructed by viewing EDX as the most significant four bytes and EAX as. As complete 32-bit data registers: EAX, EBX, ECX, EDX. The X means pair, and goes back to at least the 8080. A feature of assembly language is that each line in the source code usually contains a single instruction to the processor, for example MOV EAX,EDX will move. We can take this assembly language code, convert it to machine code using an " assembler" like nasm, and run it! mov eax,7 ret. eax is the 32-bit, "int" size register.