${?}^{\text{I}}$ A computer designer needs $2GB($GigaBytes$)$ of RAM $($random access memory$).$ Suppose that she has only several $512$ MB $($MegaBytes$)$ memory modules at her disposal. How many of these $512$ MB memory modules are needed to make up a total of $2$ GB$?[$Answer is an exact integer number requiring no rounding.$]$