DVD-r & DVD+r are incompatible in that you can't write to a +r in a -r writer and vice versa, there are writers that will do both sorts which would be the best bet. The discs look identical but are written to in a different manner. Both machines should be able to read both types of discs. There is only one standard for CDs so it wouldn't matter which ones you bought, the difference here is whether they are write once (CDr) or rewritable (CRr/w). You can also get rewritable DVDs in both -r & +r formats.