Editing Orthogonal instruction set (section)

===Single instruction, multiple operands===
Further improvements can be found by providing the address of both of the operands in a single instruction, for instance, <code>ADD ''address 1'', ''address 2''</code>. Such "two-address format" ISAs are very common. One can further extend the concept to a "three-address format" where the  <code>SAVE</code> is also folded into an expanded <code>ADD ''address 1'', ''address 2'', ''address of result''</code>.<ref name=format/>

It is often the case that the basic [[computer word]] is much larger than needed to hold just the instruction and an address, and in most systems, there are leftover bits that can be used to hold a constant instead of an address. Instructions can be further improved if they allow any one of the operands to be replaced by a constant. For instance, <code>ADD ''address 1'', ''constant 1''</code> eliminates one memory cycle, and <code>ADD ''constant 1'', ''constant 2''</code> another.<ref name=format/>