why do dvd disc say 4gb or Cd disc says 700mb but sometimes they are less than their storage capacity?

Answer 1

The disk formatting takes up space, so the actual space left over for the data is not what is labeled on the disk.

Answer 2

Those numbers are "best case scenarios", or otherwords, very optimistic. Its the same as Microsoft saying you only need 256 MB of RAM to run their programs. Technically, you could conceivably get it to load, but you won't be able to do very much else....

Answer 3

Sometimes you should buy a high quality,rather than low quality to avoid space problems