The FDC controller can be used to control 80-tracks and/or double sided drives, though AMSDOS doesn't support such formats. To use 80-track drives and/or dual-head drives, you need to use another CPC DOS instead of AMSDOS. The most popular one is [[ParaDOS]]. It can handle up to 796 KB instead of 178 KB for AMSDOSand it supports 22 different disk file formats, including the three standard AMSDOS ones.
Half of the original AMSDOS rom is occupied by [[Dr. Logo]] from Digital Research. If you replace AMSDOS with ParaDOS, you will lose access to Dr. Logo.