i recently had this problem when deciding to buy blank DVDs
my options were either +R or -R, but after much research, I believe that my conclusion was that -R was the older format meant for the early DVD writable drives
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current DVD writers will read & write for either format, while most of the early DVD players and DVD ROM drives up to 2004 only take the standard DVD-R
which actually explains alot, now that i think about the times I was having trouble trying to burn CDs around that time
as to any other differences, there isn't that much