The following information has been excerpted from Beneath Apple ProDOS by Gary B. Little, Addison-Wesley Publishing, ISBN 0-201-15008-5. According to Gary's book, the PRODOS system file uses the following memory locations: o $BF00-$BFFF in main RAM o $D000-$DFFF in $Dx bank1 of main bank-switched RAM o $D100-$D3FF in $Dx bank2 of main bank-switched RAM o $E000-$FFFF in main bank switched RAM In addition, the following memory locations are reserved by ProDOS: o $03ED-$03FF in main RAM o $D000-$D0FF in $Dx bank2 of main bank-switched RAM o $D400-$DFFF in $Dx bank2 of main bank-switched RAM The ProDOS /RAM driver uses the following memory locations: o $003C-$0043 in auxilliary zero page o $0200-$03FF in auxilliary RAM o $0C00-$BFFF in auxilliary RAM o $D000-$FDFF in $Dx bank1 of auxilliary bank-switched RAM o $D000-$DFFF in $Dx bank2 of auxilliary bank-switched RAM The following locations are not used by /RAM, but are marked as used in its bitmap. o $0400-$07FF for video RAM (in 80-column mode) o $0800-$087F for serial buffer (existing in Apple IIc only) o $0880-$08FF for keyboard buffer (existing in Apple IIc only) o $0900-$0BFF is unused, but supposedly reserved o $FFFA-$FFFF for mirroring main bank-switched RAM vectors With the /RAM driver installed, the only free locations to work with are the following: o $0000-$003B in auxilliary zero page o $0044-$00FF in auxilliary zero page o $0900-$0BFF in auxilliary RAM o $FE00-$FFF9 in auxilliary bank-switched RAM Here is a quote that immediately follows the memory locations I just listed: "Despite the apparent availability of these areas, they should be considered reserved for future use by later versions of ProDOS 8 and must not be used by nonsystem software."