Original optical disc was the CD. These CD's store data with accordence to a file system structure for either digital recorded music or plain binary data as found in a computers filesystem.
Eventually, these were improved in the past five years (to 2009) with greater capacity of data for CD'S up to 750 Mega bytes and then dual(double) sided (2x 750Mb).
The filesystem on CD's is not the same in actuallity as a hard drive or Floppy disc and there are various formats for CD's and DVD's.
Again the same is of DVD's, but DVD physical capacity and the machinery that reads them has much greater capacity than a CD and can be a double sided if specified.
DVD's and CD's have various ratings for writing data to them such as 2X , 4X ,8X and ratings for reading them with a reader only mechanism of 24X , 44X and 52Xspeeds.
Another feature that is peculiar to the writing mechanism by the software for DVD or CD is filenames. These are either able to be normal the same as a computer, or a system called jolliet filenames.
CD's and DVD's come in three basic types of RW(read and "writeable once") , direct RW that is the same as before but requires no disc formatting and organisation or also can overwrite more than once, RO or CDR read only pre constructed disc or CDRW DVDRW and can be written many multiple times.
Another final feature is an action called "overburn" that allows e.g. a 750 Mb disc to have 775 Mb of data dangerously as a possibility at burn time if the disc is well organised and will be finalised.