For CD-Rs, what does it mean by "multi-session"? I've been told that I need to "close" the disc upon recording my data unto it. Does this mean that I can save a little at a time, switch off my computer and come back another time to continue saving more data onto the remainder space? I've tried the CR-RW and it work just like a hardisk. But I'm venturing into the CD-R and I would like to know more so as not to waste any of the disc unknowingly.