What are quick, small stores of data within the CPU called?

Registers are indeed the quick, small stores of data directly accessible within the CPU. They play a crucial role in processing as they hold temporary data, instructions, or addresses that the CPU needs to execute tasks efficiently. Because registers are located within the CPU itself, they enable faster access compared to other forms of memory, such as RAM. This proximity is essential for the rapid computation and processing power of the CPU, as it allows the execution of instructions with minimal delay.

The other options refer to specific components of the CPU or memory hierarchy that serve different purposes. The Memory Data Register is responsible for holding data that is being transferred to or from memory, but it does not function as a quick store of data for processing. The Program Counter keeps track of the next instruction to be executed, which is vital for the sequencing of operations but does not store data itself. The Control Unit directs the overall operations of the CPU but again does not hold data. Therefore, among the provided options, registers are the correct answer as they are specifically designed for fast, small-scale data storage during processing tasks.