These recorders were quite expensive when they hit the market--about $900--and that was in the early 2000s.  The unit uses CF cards and can be powered by batteries or with the DC converter, which is included.  It records in mono or stereo, it accepts either dynamic or condenser mics, and it provides phantom power for condensers.  It works, and it is in good cosmetic condition.  This recorder bears a label indicating it was the property of Cornell University.  Apparently, someone used it in their Ornithology Department to capture birdsong in the field.  Marantz issued a software update for it, which is readily available online.  I haven't installed the update, but I believe it improved the self-noise in the unit.  Sold as-is.  I've tested it only to be certain it records and plays back and that the knobs and switches work, but I haven't tested it critically or extensively.  I tested it with the AC/DC wall wart, but I haven't checked it with batteries.  Consult online manual for details about features: I checked the boxes for all those I know how to check, but I'm not as familiar with all the abbreviations used to describe ins/outs/functions.  The template eBay supplied for this unit indicates it accommodates Firewire, but I don't see a Firewire port on it.