A RAM Disk is a block of memory that can be accessed as a disk device. Due to the nature how RAM works, its contents is gone after reboot or shutdown. This means anything you store on a RAM disk is gone after a reboot.
The image files are used to overcome this behaviour. An image file is a regular file on a HDD, that is read into a RAM disk to populate it with contents. Likewise, before the system restarts the contents of a RAM disk can be saved to an image file to preserve user data between sessions.
I am not sure what you want to do with the PCIe express card that you have, as this RAM disk software only uses RAM ('software RAM disk'). You can find out more about
how a RAM disk works in Wikipedia.