NASM 2.05 based x86 Instruction Reference[ch137]
A.5.117 IDIV: Signed Integer Divide IDIV r/m8 ; F6 /7 [8086] IDIV r/m16 ; o16 F7 /7 [8086] IDIV r/m32 ; o32 F7 /7 [386] IDIV performs signed integer division. The explicit operand provided is the divisor; the dividend and destination operands are implicit, in the following way: - For IDIV r/m8, AX is divided by the given operand; the quotient is stored in AL and the remainder in AH. - For IDIV r/m16, DX:AX is divided by the given operand; the quotient is stored in AX and the remainder in DX. - For IDIV r/m32, EDX:EAX is divided by the given operand; the quotient is stored in EAX and the remainder in EDX. Unsigned integer division is performed by the DIV instruction: see section A.5.59.