Digital obsolescence

Digital obsolescence is a situation where a digital resource is no longer readable because of its archaic format. There are two main categories of digital obsolescence:
The continuing rapid evolution and proliferation of different kinds of computer hardware, modes of digital encoding, operating systems and general or specialized software has ensured that digital obsolescence will be an equally ongoing problem. Cornell University Library’s digital preservation tutorial (now hosted by MIT Libraries) has a timeline of obsolete media formats, called the "Chamber of Horrors", that shows how rapidly new technologies are created and cast aside. A prime example of this problem is the BBC Domesday Project from the 1980s, although its data was eventually recovered with significant effort. 
Obsolescence in software.
Many versions of word-processing programs, data-storage media, and formats for encoding images and films were in the past considered industry standards but have since been replaced by new software versions or even by completely new hardware. Files meant to be read or edited with a certain program (for example Microsoft Word) might be unreadable in other programs, and as operating systems and hardware move on, even old versions of programs developed by the same company become impossible to use on the new platform (for instance, older versions of Microsoft Works, before Works 4.5, cannot be run under Windows 2000 or later). Some industry experts actually consider obsolescence to be a security feature in some contexts, arguing that outdated software is more difficult to hack, but this idea has not been widely accepted. Many entities now consider formatting obsolescence to be a key concern. In 2002, for example, the National Initiative for a Networked Cultural Heritage cited uncompressed TIFF and ASCII and RTF as "de facto" formats unlikely to be rendered obsolete in the near future. Charles M Dollar attempted to bring attention to challenges of preserving machine-readable data in the 1970s, but it was only during the 1990s that libraries and archives came to appreciate the scope and significance of the problem. Digital obsolescence has since become a major ongoing concern across both of these professions, and so far there is no obvious solution other than the laborious continual forward-migration of files and information to the latest data-storage standards. 
Video games are especially vulnerable to this. When the system that a game was designed for becomes obsolete the game itself is frequently forgotten entirely by its manufacturer, becoming abandonware, a kind of orphan work. Computer games have a history dating back to the 1960s, and most of the older examples of the genre are designed to be played using hardware and operating systems that are long outdated. Not only does this mean that the game becomes essentially unplayable, it can also lead to unclear or contested copyright, with ownership being claimed by or attributed to multiple individuals or entities. 
Untangling copyright issues also presents a significant challenge for digital preservation projects. A non-video game example is the BBC Domesday Project. In addition to the individual copyrights of the estimated 1 million people who took part in the project, there are also copyright issues that relate to the technologies employed. It is likely that the Domesday Project will not be completely free of copyright restrictions until at least 2090, unless copyright laws are revised for earlier expiration of software into the public domain.
Obsolescence in hardware.
Contrary to widespread belief, most data storage formats are quite durable. If properly maintained and kept in a controlled environment, magnetic or digital/optical audiovisual data can be accessed thousands of times without any perceptible loss of quality. However, replaying these files and accessing the data requires the necessary equipment to be in full working order. Even if the storage devices themselves (tapes, CDs, wax cylinders, DVDs, etc.) are in perfect working order, without the machine to read and play the data they are essentially worthless because they are inaccessible. Therefore, it is not always enough to simply preserve that data itself, organizations must also preserve all of the hardware that the data format requires. 
This is a challenge on many different levels because machines are subject to mechanical failure and need repair on a semi-frequent basis. Many machines require frequent maintenance like cleaning and degaussing in order to remain functional. Occasionally, especially in more recent devices, certain parts may need to be replaced regularly in order to function optimally, even if the part in question is still intact. In addition to maintaining machines like phonographs and VCRs, organizations must maintain stocks of replacement parts for their machines. Unfortunately, once a particular technology becomes obsolete companies generally stop making machines and replacement parts, turning instead to making equipment to support whatever new technology is now dominant. In doing this, many machines that were once commonplace become rare as there are only limited supplies of replacement machines or parts, with no new replacements forthcoming. This has actually become more of a challenge as the technology in question has become more sophisticated; while it is possible for a skilled technician to create a phonograph which works at least as well as one from 1905, it is extremely difficult if not impossible to maintain a tape recorder or digital video recorder without prefabricated parts from the original manufacturing company.
Ironically, paper documents such as books are almost entirely immune to these problems. Non-acidic paper and inks are extremely chemically stable and can last for centuries if not millennia when kept in a controlled environment. In fact, the greatest cause of obsolescence in printed media is linguistic drift, a process that can take centuries.
Strategies.
Any organization that has digital records should assess its records to identify any potential risks for file format obsolescence. The Library of Congress maintains Sustainability of Digital Formats, which includes technical details about many different format types. The UK National Archives maintains an online registry of file formats called PRONOM.
In its 2014 agenda, the National Digital Stewardship Alliance recommended developing File Format Action Plans: "it is important to shift from more abstract considerations about file format obsolescence to develop actionable strategies for monitoring and mining information about the heterogeneous digital files the organizations are managing." 
File Format Action Plans are documents internal to an organization which list the type of digital files in its holdings and assess what actions should be taken to ensure its ongoing accessibility. Examples include the Florida Digital Archive Action Plan and University of Michigan's Deep Blue Preservation and Format Support Policy.
Open source software is often cited as solution for preventing digital obsolescence. With the available source code the implementation and functionality is transparent and adaptions to modern not obsolete hardware platforms is always possible. Also, there is in general a strong cross-platform culture in the open source software ecosystem, which makes the systems and software more future proof.
Open standards were created to prevent digital obsolesce of file formats and hardware interfaces. For instance, PDF/A is an open standard based on Adobe Systems PDF format. It has been widely adopted by governments and archives around the world, such as the United Kingdom. The Open Document Format for Office Applications (OpenDocument) has been standardized by OASIS in 2005, and by ISO in 2006.
On 30 November 2017, the Digital Preservation Coalition released The 'Bit List' of Digitally Endangered Species, identifying file formats at risk, as part of an international campaign to raise awareness of the need to preserve digital materials on the first International Digital Preservation Day.