The future accessibility of data files is dependent on a number of factors. Digital storage media formats will become obsolete over time – remember floppy disks?! – and their usefulness depends on the quality of the storage medium and the availability of the relevant data reading equipment (e.g. software).
CDs, DVDs, and other optical media are vulnerable on a number of fronts: changes in temperature and humidity, poor air quality or lighting conditions. The National Preservation Office has published guidelines on Caring for CDs and DVDs.
Magnetic media, like hard drives or tapes, are also subject to physical degradation and should be regularly migrated to fresh media. It is recommended that for any project, at least two different forms of storage (e.g. hard drive and DVD) are employed, and that the data integrity should be checked periodically. Flash drives and solid-state drives will also degrade over time.