Long-term storage and availability of digital data is determined by various factors which are listed below.
Lifespan of data carriers
All important data carriers in the history of mankind have a considerable lifespan. While stone tablets survive for several millennia, books made of acid-free paper after all may live for several hundreds of years. In contrast, optical storage media such as CDs and DVDs will at best last for 80 years if they are stored under good conditions. If stored improperly, the may not even survive six months. In most cases, this also goes for USB sticks.
Availability of reproducing device
Often, data is stored on carriers which are obsolete (e.g. 5¼'' floppy disc drive). Such data carriers in the possession of a cultural heritage institution raise a multitude of questions. New devices cannot access them and replacement parts for old devices are difficult to obtain.
Operating and file systems
The operating system used to run modern computers determines the file system (e.g. FAT12, NTFS, EXT3,…) of the computer. Not all operating systems can interpret all file systems. However, if the file system can no longer be interpreted, the information on the data carrier can no longer be read.
Moreover, appropriate knowledge of how to handle the respective operating system is required.
Incompatibilities and "ageing" of software
The software used to create or display digital objects also represents a risk. The software has to be available to display the data. This often is not possible especially in the case of old software. The next problem is that often the software cannot be installed on modern operating systems.
Incompatibilities and "ageing" of formats
Formats are an important issue with regard to digital preservation. This is made clear, e.g. by their prominent position in the OAIS reference model.