The Symbiface 2 operates the ATA/IDE device in 16-bit data transfer mode. 16-bits of data is buffered at a time within the Symbiface 2 and read /written via the Data port below I/O address 8 bits at a time. The device was designed when devices didn't support ATA CFA command set and 8-bit PIO data transfer so this is why it buffers 16-bit of data. (16-bits is the "native" data transfer of an ATA device).
The I/O ports operate in a "pass-through" like mode where the registers directly reflect those of the connected ATA device.
The [[X-MASS]] is a more modern ATA/IDE device which is compatible with the Symbiface 2 IDE registers and uses the same I/O ports.
This is the documentation about the '''IDE registers''' of the [[SYMBiFACE II]] expansion card.