Once you encode data, it is critical that you remember the
encoding.

Digital obsolescence

https://dpworkshop.org/dpm-eng/eng_index.html

Physical media. - the media data is stored.
  e.g 8 inch floppy,  magneto-optical.
  Punch card, tape drives, 8" floppy, 5 1/4" floppy, 3 1/2" floppy, etc.

Encoding on media - how bits represente, NRZ, NRZI, MFM, etc.
  Size and format of data 
    Size of byte, size of block and error correction.
    ASCII, EBCDIC, size of integer or float, etc.

Hardware - actual hardware to access the media.

Interface with system - device drivers, ports.

Software - higher level encoding.
  Meta data - data about data in data (think html)
    ASCII, Unicode, html, custom floating format.
    * anyone come across an old WordPerfect file.

Copyright issues.