Hi, today I backup my files into a 700Mb CD-RW cd. However, the size of all my files are around 690mb, so my burning software told me something like this: "Your cd doesn't have enough space, do you want to finalize it in order to be able to continue" I click YES. then it burns successufully. However, I learned that once the cd is finalized, we cannot add more file anymore...but can we erase it and put files again? Thanks

If the cd that is finalized is cd-rw, then you can format the entire cd to use it again. I am fairly sure you cannot add files to a finalized cd-rw. If the cd is cd-r, than you cannot ever erase files on the disk, finalized or not finalized. When storing or transferring data such as documents, pictures, or mp3, I prefer not to finalize, so I can add more data to the disk later. Otherwise, the empty space of the cd is wasted, but cd-r are not expensive these days, anyway.

If the disk is only to be used on your machine then don't bother finalising. Your machine will still be able to read the disc, but you may run into trouble if you want to use it in anyone else's machine unless they have the same software as you. As for using CDRW for backup, you might consider switching to using CDR instead. AFAIK CDRW discs will readily pick up and transmit viruses just like your hard drive.