i 'm new mac user,i can't write/copy again on my cd-r after burn my cd-r.it was use 50 mb so it still have 650 mb

CD-R is a single session Recordable CD. Audio CD's and most Application CD's are burned on CD-R. You record the files and then the CD is closed/ locked and cannot be added to or deleted from. CD-RW is a Multi-Session Re-Writeable CD that is formatted before use and can be used much like a Floppy BUT you must use the burner software to make the changes to the CD-RW. Not all MP3 players can read CD-RW but all can read CD-R if they are in the ISO 9660 format. I have found that CD-R is more in line with every day use and have given away all my CD-RW discs. The average cost of CD-R when purchased in bulk of 100 has been about 20 cents each. New technology. Toast Titanium 5 allows multi-session writes on a CD-R and does not require formatting a CD-RW before use. Well worth the money.