Fons Adriaensen: Sure, it was an immature way to answer. But since there are a number of reasons why writing simultanious data or zeros could be faster, it would make sense to write something other than just the most obvious. I do of course think that it's pretty unlikely that zeros are faster, but I wouldn't have added the "(?)" if I had known "exactly how it works". (which is what I wrote, not "not knowing how it works") Well, thanks for correcting me anyway.