Registers are small pieces of memory on the CPU die that can be used to store data $($or bit patterns that

can be interpreted as data or instructions$)$ in the very near term. There are various "things" involved

in creating a program to be executed on a CPU. These "things" include:

$($a$)$ The software developer who designs the algorithm

$($b$)$ The software developer who uses some IDE to create a program source file$($s$)$

$($c$)$ The source file compiler that converts the source file to an object or executable file $($depends on the

compiler$)$

$($d$)$ The operating system that loads the executable file from disk into RAM and tells the CPU where

it is$,$ so the CPU can start execution

$($e$)$ The CPU that is executing the program

Which of these things decides how the registers are used?