Actually pioneerelectronics does have some info on it right here.
Or you can do a Google search for pioneer deh-840mp or another model in that series.
From pioneerelectronics.com:
MP3 Playback / 10GB Hard Drive / OEL
DEH-P90HDD
MP3 / WMA Playback / OEL
DEH-P9400MP
DEH-P940MP
MP3 / WMA Playback with Dual Motorized Faceplate Design / OEL
DEH-P8400MP
DEH-P840MP
MP3 Playback / OEL
DEH-P7400MP
DEH-P740MP
Single CD / OEL
DEH-P6400
DEH-P640
Single CD
DEH-P4400, DEH-3400, DEH-2400F, DEH-1400
DEH-P440, DEH-340, DEH-240F
Or you can do a Google search for pioneer deh-840mp or another model in that series.
From pioneerelectronics.com:
MP3 Playback / 10GB Hard Drive / OEL
DEH-P90HDD
MP3 / WMA Playback / OEL
DEH-P9400MP
DEH-P940MP
MP3 / WMA Playback with Dual Motorized Faceplate Design / OEL
DEH-P8400MP
DEH-P840MP
MP3 Playback / OEL
DEH-P7400MP
DEH-P740MP
Single CD / OEL
DEH-P6400
DEH-P640
Single CD
DEH-P4400, DEH-3400, DEH-2400F, DEH-1400
DEH-P440, DEH-340, DEH-240F