This animation demonstrates the process of the CPU requesting a "Write" operation to memory. The address of the datum to be written is currently part of the instruction, stored in the IR (for instance, Store x). The datum to be stored is currently stored in the AC. The address of the datum (x) is sent from the IR to memory, the datum is sent from the AC to memory over the data bus, and the control unit signals a "memory write". Memory takes the datum and stores it in the address as indicated by the address sent over the address bus. This is an animation of figure 2.5b from the textbook.