Welcome to the arcane world of computer memory and storage, a sometimes confusing but critical set of concepts. When you're out of memory or out of storage, you're out of business. Hard drives, floppies and Zip disks are all storage.
Rewritable CDs are a hybrid of optical and magnetic technologies.
Unlike most CDs, these discs, called CD-RW, can bereused. Memory is a working copy of something you type in from your keyboard or that is on a storage device. The key element is that memory is temporary and things remain in memory only as long as your computer is on. The smallest unit of measurement is the bit, which represents either a 1 or a 0, the two digits which make up the language of computers. On magnetic media, like hard drives and floppy disks, small areas of the disk are magnetized.