How do I know if the blank CDs & DVDs I buy are rewritable?
Answer: Blank CDs come in two varieties -- CD-R and CD-RW discs. CD-Rs are recordable CDs, meaning they can record audio or data only once. CD-RWs, on the other hand, can record data multiple times. But to re-record data on a CD-RW disc, you must completely erase it first. Because CD-RWs can be rewritten, they do not hold data reliably for as long as CD-Rs do.
Writable DVDs come in more varieties than CDs, including DVD-RAM, DVD-R, DVD+R, DVD-RW, and DVD+RW. DVD-R and DVD+R discs are nearly the same thing, but are formatted differently. The same is true for DVD-RW and DVD+RW discs. DVD-RAM discs are seldomly used anymore. Like CD-Rs, DVD-R and DVD+R discs can be written to only once, but have more reliable data integrity than rewritable DVDs. DVD-RW and DVD+RW discs can be rewritten, but they must be erased each time you want to record new data on them.
To summarize, look for discs ending in "-R" if you want single-use recordable CDs or DVDs. Look for "-RW" if you want discs that you can use more than once. Recordable (-R) discs are a good choice for burning audio CDs and making DVD movies. If you need media for making frequent backups, it make sense to buy rewritable (-RW) discs.