aquabelle,
The MFD12 operating system is stored and executed from solid state memory. The charts are stored on a high G industrialized hard drive. Deleting un-needed charts is a great idea for making room for SAT photos or other needed charts, but it will have little to no effect on the boot up time of the unit. If you find yourself waiting for boot-up, it sometimes pays to make the power up as part of your boat prep. The unit can always be put into "SLEEP" mode to save power until you are ready to use it. The time from sleep to operation is almost instantaneous.
Johnny