Officially there are only floppy controller cards, with a WD floppy controller chip in their heart.
But around those cards, they built a software functionality (called EXDOS) which can communicate the floppy controller cards, and above that, this EXDOS can handle FAT12 filesystem (standard PC floppy filesystem from that ages), and has a command interpreter (a shell like thingy) focused on the high level file functionality (like copy, rename, move, ramdisk, etc.).
This EXDOS implemented on the top of the EXOS. EXOS is the OS of the EP.
And this EXDOS is extendable. It has a layer, what can be implemented by hardware devices, and from that point such devices can be EXDOS devices, too. Every EXDOS functionality will work on those hardwares, too.
Using this layer, there is an IDE controller card created by Zozosoft, and into that IDE card you can connect IDE devices, like a HDD, or an IDE to CF converter, or what you can convert from IDE.
There is a cartridge SD solution, what works on the same EXDOS extension layer:
http://szergitata.blog.hu/2014/07/13/enterprise_128_sd_adapter_quick_start_guide_ukAnd there is an under construction EXPANSION port device (the right side of the EP) combined with RAM and ROM extension, too:
http://enterpriseforever.com/hardware/sd-card-interface/