Those links certainly help in highlighting the difference. Of course, the answer depends on what you mean by modernism and post-modernism. As far as I have learned, there is modernism in art, philosophy, theology, historical studies, and sociology.
I can primarily speak a little on modernism and post-modernism as a philosophy since that is where I am well-read. The difference between the two can be described in terms of history and perspective. However, it can only be done with great difficulty since there was not a single comprehensive system of modernism to which we may point. There were different thinkers with different philosophies that were identified as champions of modernism. Their thoughts could not be synthesized as a whole nor reduced to a common foundation.
But, like a philosopher, I’m going to try anyway.
What we can say is that modernism preceded post-modernism. What was common in modern thought was that all of reality may be accounted for through rational thought freed from personal prejudice and cultural presuppositions, such as emotions and religion. Then this rational thought could be applied through the naturalistic scientific method. In a sense, great faith was placed in what we now call, “science.”
Post-modernism calls this entire project into question because even when one tries to set aside subjectivity in viewing reality, one is still looking at reality through the prejudice of their own subjectivity. Thus, even science as a supposed objective pursuit is still enslaved to subjectivity. For that matter, even the question about what is real is projected from the subjectivity and inter-subjectivity of the human creature. In essence, post-modernism concludes the deconstructive arguments of modernism through a radical skepticism that cuts away any kind of foundation by which people can say they know or see anything.
This is a very cursory summary that I would make about the difference between the two. I will certainly now be flamed by other philosophers in this forum.