Dunno about the PC writer ones but using a DVD-R on a home DVD recorder such as the Panasonic once you hit the STOP button when recording the programme is finished and you can not record as a continuation. The disc isn't finished until you finalise it so you can then record again starting a new programme. You can continue doing this until the disc is full recording at speeds from XP to ELP (1 hour to 8 hours to fill the disc). Once the disc is full you can not record any more progs and the disc needs finalising to be able to play on a domestic DVD player. You can leave the DVD recorder on pause for quite a long time when recording a programme onto DVD e.g. for finding a different part on a VHS tape to record or even to replace the VHS tape by another one to carry on recording the same DVD section without pressing the STOP button. You can also do the same with DVD-RAM discs which are re-recordable over and over again.
Further note on home DVD recorders. You can leave a disc unfinished for as long as you like and return to it again later. I have several discs on the go at present with spare space for more recordings. I also mix quality settings on discs by using mainly SP and LP settings (you can do this on the same disc - until its capacity setting is reached).
You can create a multisession with a DVD R disk the same as a CD disk. With Nero when creating select Start multisession. When adding to a multisession you must select continue multisession this add to the first session.(Do not select start multisession as you will have problems seeing the first session). When you have finished the disk remember to close the disk.