Step 4 - Adding an instruction A new window opens as soon as the new instruction is selected. An helpful description, especially when the developer is still fresh to MMX programming, appears by clicking on the Help button.  The assumption that the EAX register points to the first source image is made, thus you should click on Memory as Source operand and type [EAX] in the edit box on the right (1). Now this data should be placed in the MMX variable called SourceImage1, so you should choose MMX variable as the destination operand and SourceImage1 from the drop-down box on the right (2).  Since the desired instruction is fully specified, pressing the OK button will confirm the addition of this instruction to the source code. The first MMX instruction appears in the source list. The next step is repeating the same operation loading the first 8 bytes of the second source image into SourceImage2 and performing the absolute difference.