In this situation, the codice_18 instruction on line 2 is not ready to execute, but the codice_19 instruction on line 3 is ready. If the processor allows the codice_20 instruction to execute before the codice_21, the load will read an old value from the memory system; however, it should have read the value that was just written there by the codice_21. The load and store executed out of program order, but there was a memory dependence between them that was violated.