I think what it means is to use an extraction (unzip) program to break out the individual files (.vob, etc.) and then reauthor by recombining these to make a new single ISO.

I'm not familiar enough with .vob and other files to be more specific.
Maybe Bob would be able to tell us if this is practical to do.

An ISO file is an archive (disk image) of an optical disk (i.e. CD, DVD, or Blu-ray). Like a backup hard drive archive, the ISO file contains everything necessary to restore the contained disc image to a new optical disk. Because the ISO file contains the file system as well as the data, you can only restore a single ISO image to a disk.

The article Peru linked is discussing the extraction the files contained in multiple CD iso images and then writing the extracted files back to a single CD. That works for CDs, but not for DVDs or Blu-Rays. The reason being that DVDs and Blu-rays don't contain arbitrary files that can be extracted and mixed. They have a well defined file system and directory structure and a specific naming convention that DVD and Blu-Ray players depend upon to find and play the menus and movies. There are also internal pointers contained in the files that point to specific locations. You can't arbitrarily rename and combine them.

However, If you just want to use the DVD or Blu-Ray disk as storage and not be a playable movie, you can burn the individual iso files to the DVD or Blu-ray as a data disk. Imgburn can do this.

Thanks for that, Bob.

BTW, I stil don't understand the difference between a "regular" and a data disk. The other day, when I was re-running PC Doctor correctly (stopping working while running it), the program asked me to insert data CDs for the purpose of checking my optical drives. I inserted a blank CD-R and got back as message "that's not a data CD."

So I ended up not testing the drives.

A blank CD is like an unformatted hard drive -- no file system and no data. To run the tests, it needs a disc formatted with a file system it can read and contain files. Don't use a commercial music CD -- those can be written in a specialized format that isn't suitable -- but almost any other CD should be fine.

A data cd is a cd that contains data.

I think it was asking for a cd that contains data that it could read, not a blank one.