How do you erase a cd-rw?

[helpneedi]

hi, i want to put information on a cd-rw, i have already put a bit, but the disk is not full. I can't put more data on top. Do i first have to erase the old data; how do you wipe a cd-rw?

 

[bunga]

Use disk utility to erase the disc, but if you want information off the disc, copy it to the hardrive first

 

[michaelsanford]

Are you sure it's a CD-RW and not just a CD-R ?