About using the “system” of the C64. This system is located in the Kernal ROM and the Basic ROM.
The KERNAL and BASIC ROMs (and the IO area, used to access the VIC and the SID) can be switched in and out, depending on whether you want to access the ROM chips, or the RAM “behind” the ROM chips. To see how to do this switching, consult the memory configuration section.
More information on diskdrive/tape etc programming is available in the IO programming section of this site.