There were a variety of proprietary “Portable-studio” type devices that were manufactured starting in the 1980s and may still be manufactured.
These devices used a wide variety of storage media from ZIP disks to hard drives as well as Mini-Discs.
Since these may use extremely proprietary formats (either for the sake of increasing performance, or locking the customer into a particular brand, or both) my best advice is that the machine is part of the record and should be treated as such.
Copying the information out of this proprietary format should be a high priority for any collection that has anything in these formats.
Related pages: Digital Audio Tape, Digital Audio on Video Cassettes