In my first 6303 based computer I used floppies for secondary storage. Even though it worked very well floppies are relatively small, fragile, slow and, above all, they are outdated. Today there are easier and more convenient ways of storing large amounts
Compact Flash + 8255 interface card.
GitHub - monotech/monotech_xt-cf-mini: Miniature 8-bit ISA CompactFlash Interface + Boot ROM
MCP3008 - 8-Channel 10-Bit ADC With SPI Interface : ID 856 : $4.50 : Adafruit Industries, Unique & fun DIY electronics and kits
FC1306T Datasheet, Chip Controller.
64MB bootable CF card Included, Bootable XT-IDE with rear accessible CF card slot, expansion card provides a Compact Flash card interface to 8-bit ISA
XT-CF - Bootable 8-bit ISA CompactFlash - XT-IDE With Slot 8 Support
Compact Flash + 8255 interface card.
ISA CompactFlash Adapter - IDE for 8-Bit PC, XT CF LITE 4.1, XTIDE. This card allows connecting a Compact Flash (CF) card to computers with ISA bus
ISA CompactFlash Adapter XT-IDE for 8-Bit PC, XT CF LITE 4.1, XTIDE Bootable
CompactFlash - Wikipedia
Compact Flash 128mb 256mb 512mb CF Card 1GB 2GB 4G Memory Card for CNC IPC Numerical Control Machine PCMCIA Adapter (2GB Compact Flash to PCMCIA) : Electronics
Simtec 8-bit IDE interface for Acorn A30x0
64MB bootable CF card Included, Bootable XT-IDE with rear accessible CF card slot, expansion card provides a Compact Flash card interface to 8-bit ISA
XT-CF - Bootable 8-bit ISA CompactFlash - XT-IDE With Slot 8 Support