On this site, I had previously posted a set of 24 Yamaha DX100 synth patches for download. The DX is a notoriously difficult synthesizer to program. That difficulty extends to its load/save workflow as well. Originally, the DX100 came with a special cord with a MIDI-style plug on one end and three headphone-sized jacks on the other. This is meant to be plugged into a data cassette recorder. The red cable is audio out, the white is audio in, and the black (I assume) controls the tape player. You hit a button combo on the DX100 and then a screeching modem sound is output to the tape. Modern users can record this sound on a computer as a .WAV file and it will work the same as and old-school tape deck. This works okay, but there is a better way to archive and reload sounds.
Sysex stands for system exclusive and it's a part of the MIDI standard that allows synth manufacturers to define their own specific message formats. In our case it is useful because the DX100 uses sysex to store and retrieve patches. With some free software and a cheap hardware interface, you can easily store and retrieve synth sounds on your PC as both individual patches and a complete 24 patch bank.