When CSC-1 performs ADD 3570, the effect is to add the contents of the A register to the contents of the memory word addressed by 3570, and to store the sum back into the A register. We can write this more succinctly in the following language:

A <- A + m[3570]

This form of writing down the function of the ADD instruction is called RTL, or register transfer language, since it shows the transfers of data from one register to another.