Final answer:
Register variables are used by system programs to minimize main memory references by optimizing register use. By storing frequently used variables in CPU registers, programs can improve performance by reducing the number of memory accesses.
Step-by-step explanation:
The registers that are used by system programs to minimize main memory references by optimizing register use are called register variables.
Register variables are variables that are stored in CPU registers rather than main memory, allowing for faster access. By storing frequently used variables in registers, system programs reduce the number of memory accesses, which can significantly improve the performance of the program.
For example, in a loop that iterates over an array, instead of accessing the array elements from memory each time, the program can store the array index in a register variable and use it directly. This eliminates the need for repeated memory accesses.