The primary step is to start the Debug; this step only consists of typing debug [Enter] on the operative system on time.
the "a" (assemble) command is used To assemble a program on the Debug, while this command is used, the address where you wish for the assembling to begin can be known as a parameter, if the parameter is omitted the assembling will be started at the area specified by CS: IP, usually 0100h, which is the area where programs with .COM extension must be
initiated. And it will be the position we will use since only Debug can create this particular type of programs.
Though at this instant it is not needed to give the "a" command a parameter, it is recommendable to do so to avoid problems once the CS: IP registers are used, consequently we type:
a 100[enter]
mov ax,0002[enter]
mov bx,0004[enter]
add ax,bx[enter]
nop[enter][enter]
What does the program perform? Ttransfer the value 0002 to the ax register, Transfer the value 0004 to the bx register, add the contents of the ax and bx registers, the instruction, no operation, to finish the program.