is the UJ-816 DVD drive a CD-RW writer ?

[Dr. Trevor J. Hutley]

I have been using the UJ-816 DVD drive in my 15" Al-Powerbook to 
write DVD-R and CD-R.

Now, I am interested in using CD-RW disks.  My understanding is that 
I can write to this kind of medium, then erase the content later. 
For example, if I want to use the CD-RW disk to transfer data to a 
colleague, but do not want to archive that data.....

So yesterday, I bought some CD-RW disks (Sony).

I just burnt a few files on one of them, just as a test.

But they now seem permanently on the CD.

I am now wondering whether this UJ-816 is a CD Rewritable writer, or 
whether it simple treats CD-RW as CD-R disks.

Or am I doing something worng?
Is there something else, not obvious, that I should be doing to use 
the CD-RW capability?

Sorry if these seem very simple questions, but this has kind of taken 
me by surprise.

Trevor