Track At Once – data are written to the CD-R one track at a time but the CD is left "open" for further recording at a later stage. It also allows data and audio to reside on the same CD-R.[6] Packet Writing – used to record data to a CD-R in "packets", allowing extra information to be appended to a disc at a later time, or for information on the disc to be made "invisible". In this way, CD-R can emulate CD-RW; however, each time information on the disc is altered, more data has to be written to the disc.