Which register in the CPU holds the address of where the next instruction is located?

The register that holds the address of where the next instruction is located is the Program Counter. This register is crucial in the instruction cycle of a CPU because it ensures that instructions are executed in the correct sequence. Every time an instruction is fetched from memory, the Program Counter increments to point to the next instruction's address, which allows for the continuous flow of instructions being processed by the CPU.

In contrast, the Memory Data Register holds data being transferred to or from memory, while the Control Unit orchestrates the operation of the processor and manages the execution of instructions. The Accumulator, on the other hand, is used to store intermediate results of arithmetic and logical operations. By focusing on the function of the Program Counter, it is clear why it is the essential register for keeping track of instruction execution flow.