I know you said "digital" ...

Before digital hit the photography scene, we archived our data by microfilming to 16mm roll film, and to fiche for A4 documents; and a larger version, Aperture Cards (thin card about 8" x3" with a window), were used to hold a photograph of drawings up to A0. They're still available:-

See here

We used early databases to record what was on which film etc. and where stored. The beauty of any non digital method of recording is that the archival properties of the technique are well researched, and you're not at the whim of a change in digital OS / standard. In extremis an optical microscope can see what the data is.