Technical obsolescence affecting digital materials arises from two sources: hardware or storage media on which the information is encoded and software systems (and the formats) that render the bits interpretable by other systems that are, in turn, comprehensible to users.
The storage media itself — such as optical discs or hard drives — may degrade, making the stored information irretrievable. Digital formats, systems, and hardware advance, and older systems may no longer be supported. If the content is not copied and migrated to new, supported formats and hardware before obsolescence in any one of these elements occurs, then the content may become irretrievable and inaccessible. There is little gray area with digital storage; unlike analog media, if digital media degrade, they do not remain partially perceivable, but generally become completely inaccessible.