I am unable to write to the full size quoted on the disc. Why is this?

• There is various reasons why the size of the disc can't be reached.
• The main one being confusion over the labelling of discs.
  One kilobyte is 1024 bytes, and one Megabyte is 1024 kilobytes.
  One megabyte on a hard disk is 1024 x 1024 bytes = 1,048,576 bytes.
  If you store 700mb on a CD, that is 700 x 1,048,576 bytes of hard diskspace, which would equal 734,003,200 bytes of hard disk space
• We leave a small margin for universal compatibility, so we quote 730MB
• It can depend on the size of the files. If you have a few big files, you can fill up the disc quickly. If you have many small files, the index tables will take up a lot of space.
• Most writing programs will set aside some space to organise the disc to their liking. This generally causes the disc size to be slightly less than stated.

Link:
www.medea.co.uk/techsupport/index.php?action=kb&print=46