Determine physical address in the real mode of the following

Determine physical address in the real mode of the following instruction MOV [BX + SI + 90AOH], CX

Solution

Firstly given data:

DS -> 1000H

BX -> 789AH

SI -> 5000H

CX -> 1234H

Now instruction is [BX + SI + 90A0H]

This instruction is wrappped around square brackets, so we need to multiply registers with 16.

[BX + SI + 90A0H] ======> 16 * 789AH + 5000H + 90A0H ==> 16 * C89A + 90A0H ==> 16 * 1593A => 1DAAFC

CX -> 1234H (directly given in question itself).

So the physical addresses are 1DAAFCH and 1234H