Yamaha dx100 Owner's Manual page 40

If you choose to program a voice from scratch, you'll need to have a clear memory
location (or one containing a voice that you either don't want or have already backed
up on cassette tape, so that when you've completed programming the voice, you
can save it). Since all editing is done in the separate voice edit buffer, nothing is
erased while you are actually programming the voice. But when you save the new
voice, whatever was in that memory location will be erased and replaced by the
new data.
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