In CD-Rs, a laser recorder copies data on a blank
CD by selectively burning an organic dye on the
CD surface. This process is also known as burning and it is a permanent and irreversible process.
CDs burnt by a
CD-R can be used only once. But with
CD-RW's, a laser recorder melts an alloy on the surface of the
CD in selective degrees. This is a reversible process and these
CDs can be used for around a thousand rewrites.