It is not possible to format a CD-R disc. However, you can format CD-RW discs by using the built-in formatting tools in Windows and Mac OS X operating systems.
To format a CD-RW disc on a Mac OS X system, place the disc in the CD/DVD drive, and launch Finder. Navigate to the Applications folder, open Utilities, and click Disk Utility. Once the application opens, select the disc from the list on the left, click the Erase tab, and then click the Erase button at the bottom right.
If using a Windows computer, click the Start button on the lower left, and click Computer. Open the disc, and click Erase This Disc on the toolbar at the top. Type a name for the disc, choose a disc type, and click the Next button.
When formatting a CD-RW disc, Windows offers two options: you can format it as a Live File System disc or as a Mastered disc. A Live File System disc allows you to treat the disc like a USB flash drive. You can drag files into the disc and update files individually. In comparison, a Mastered CD-RW disc acts identical to a CD-R disc but is compatible with a greater variety of operating systems.
CD-RW discs have limited lives. Formatting a CD-RW disc too often causes it to become unusable.