This animation demonstrates the process of the CPU requesting a "Read" operation of memory. The address of the datum to be read is currently part of the instruction, stored in the IR (for instance, Load x). The address of the datum (x) is sent from the IR to memory and the control unit signals a "memory read". Memory looks up this address and sends the datum back to the CPU over the data bus. The datum is stored in the AC. This is an animation of figure 2.5a from the textbook.