Not much known.
Reportedly, the RAM is accessed in 128-byte sectors.
That, probably via I/O ports, ie. unlike other RAM expansions, the RAM is probably not mapped to the Z80 memory region.
I/O Ports
#F9FC - #F9FE Otten & Fecht 1 MB RAM-Disc (R/W) #FBF0 - #FBFF Otten & Fecht 1 MB RAM-Disc (R/W)