That rule of thumb is from Jim Gray: http://en.wikipedia.org/wiki/Jim_Gray_(computer_scientist) http://en.wikipedia.org/wiki/Jim_Gray_(computer_scientist) It'

That rule of thumb is from Jim Gray: http://en.wikipedia.org/wiki/Jim_Gray_(computer_scientist) http://en.wikipedia.org/wiki/Jim_Gray_(computer_scientist) It's held true for a long time. Like any rule of thumb, at some point it may no longer be correct, but we're not at that point yet.