Can a blu-ray DVD play on an old DVD player or does the DVD player HAVE to be blu-ray compatable?

I want to get the software DVD Suite Ultra 7, however it says that it burns blu ray DVDs. If I end up burning blu ray dvds I want to make sure that I am able to watch them on a regular DVD player

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3. Can a blu-ray dvd player play normal DVDs as well as blu-ray dvds?
4. BLU RAY – Can you play regular DVD on a Blu Ray player?
5. can an hd/blu ray dvd play on a regular dvd player and still have the same picture quality?