Ready Boost can use 1 or more allocated drives (like usb sticks) to store the data over the capacity of you free RAM needed by Superfetch. RB is a the supplement to the Superfetch. This way Ready Boost stores what Superfetch cannot store in RAM (due to RAM shortage), and it can boost applications start by 1-3 %. RB is in no way to increase the amount of your free RAM, it is to cache the data often used by programs.