Hi Peter. It depends on how you created the disk. As you know RW disks can be written to many times, but whether you can add data to a specific disk or not depends on how you created the data that is already on the disk.
Assume a blank formatted disk to start.
1. Using something like Pinnacle Instant Write you can drag and drop files from your HDD to the RW disk in a very similar way as if you were copying files between folders on your HDD. Using this method means that Folders and Files on the RW disk can be managed exactly as you would manage them on your HDD.
2. Again assuming you use something like one of the Pinnacle disk products, you can "Create a Disk". When you do this you normally create a Project and then place into that project the actions that need to be written to disk. Once a disk is created in this way you cannot add or delete individual elements from the disk. The disk can be seen as a complete entity. You can of course reformat the disk and write another project to it.
Follow this link click here and then click on TUTORIALS. This will help you understand how DVD/CD disks can be created and managed.