Can someone explain "non-rewriteable" CDs to me?

Can someone please explain "non-rewriteable" CDs to me? If they are supposedly "non-rewriteable", then why does it work to add new files to the CD as long as I am adding the files on the same computer that I originally used when I first place other files onto the CD?

In other words:

the first time I put some files onto the CD, I used computer A. Then a month later, I again used computer A and put a new file onto the same CD, and it worked, I can use that file from that CD from computer A. (even though the CD is "non-rewriteable".) However, if I take that CD and put it into computer B, all I can see are the original files on the CD, I cannot see the new file.

Is this on purpose by CD manufactuers? Yet I can rewrite all I want as long as I use the same computer, apparently? Tweet