We will reveal the fundamental and practical limits on speed and energy dissipations of magnetic writing with the help of light. Here we aim to push the existing borders down to the frequency of magnons at the edge of the Brillouin zone (THz) and the fundamental Landauer (10-23 J/bit) or the practical limit of energy dissipation per bit in a superconducting transistor (10-19 J/bit single flux quantum pulse).