Digital Media Preservation and Conservation Techniques: Digital preservation is defined as a long-term, error-free storage and management of digital information, with means for retrieval and interpretation. Digital preservation requires more constant and ongoing attention than preservation of other media. This constant input of effort, time, and money to handle rapid technological and organizational advance is considered the main stumbling block for preserving digital information. Indeed, while we are still able to read our written heritage from several thousand years ago, the digital information created merely a decade ago is in serious danger of being lost, creating a digital Dark Age. The following two terminologies are used in conjunction with digital preservation
a) Digital Curation: Digital curation is the selection, preservation, maintenance, and collection and archiving of digital assets. It is the process of establishing and developing long term repositories of digital assets for current and future reference by researchers, scientists, and historians, and scholars generally.
b) Digital Obsolescence: Digital obsolescence is a situation where a digital resource is no longer readable because the physical media (modes of digital encoding, data –storage medium, standards for encoding images and films), the reader required to read the media, the hardware, or the software (operating systems and general or specialized software) that runs on it is no longer available.
Digital technology is developing extremely fast, and one retrieval and playback technology can become obsolete in a matter of years. When faster, more capable and cheaper storage and processing devices are developed, the older version gets replaced almost immediately. Even different computer "standards" are only for some time, and in the end are always replaced by new versions of the software or completely new hardware.
Only continual forward-migration of files and information to the latest data-storage standards can address the issue of digital obsolescence. File formats should be widespread, backward compatible, often upgraded, and, ideally, open format. The National Initiative for a Networked Cultural Heritage cites uncompressed Tagged Image File Format (TIFF) and Portable Document Format (PDF) (for images) and American Standard Code for Information Interchange (ASCII) and Rich Text Format (RTF) (for text) as “de facto” formats that are unlikely to be rendered obsolete in the near future.
The preservation of digital media includes the following techniques-
a) Avoiding Physical Deterioration of Media: The media on which digital contents are stored are more vulnerable to deterioration and catastrophic loss than some analog media such as paper. While acid paper is prone to deterioration in terms of brittleness and yellowness, the deterioration does not become apparent for at least six decades; and when the deterioration begins, it progresses slowly. It is also highly possible to retrieve all information without loss after deterioration is spotted. The recording media for digital data deteriorate at a much more rapid pace, and once the deterioration starts, in most cases there is already data loss. This characteristic of digital forms leaves a very short time frame for preservation decisions and actions. So it should be avoided as far as possible by maintaining an appropriate environmental condition.
b) Refreshing: Refreshing is the task of transferring contents between two types of the same storage medium. Sometimes transferring the data from one long term storage medium to another is also termed as refreshing. It addresses the issues related to media obsolescence. Examples include transferring contents from floppy to CD and then to DVD and then to Blue ray and so on. Transfersing census data from an old preservation CD to a new one is also one example of refreshing.
The refreshing strategy may need to be combined with migration when the software or hardware required to read the data is no longer available or is unable to understand the format of the data. Refreshing will always be necessary due to the deterioration of physical digital media.
c) Replication: Replication is the process of creating multiple copies of the digital document and keeping them in multiple locations. Sometimes it is the best means of preserving cultural resources by lowering the risk of loss. Data that exists as a single copy in only one location is highly vulnerable to software or hardware failure, intentional or accidental alteration, and environmental catastrophes like fire, flooding, earthquake, etc. Digital data is more likely to survive if it is replicated in several locations. This goal may be facilitated by following standards and guidelines that mandate producing a master copy for long-term storage and preservation, and producing used copies derived from the master copy in the format that best satisfies the users’ needs.
d) Bit-stream Copying (Backing up data): Backing up data refers to the process of making an exact duplicate of the original digital object and it should be followed by remote storage so that the original and the copy document does not become victims of the same disastrous event. This is an essential preservation strategy for data loss due to hardware and media failure, normal malfunction and decay, malicious destruction or natural disaster.
e) Migration: The biggest problem to the digital media preservation is the storage format evaluation and its obsolescence. Migration can address this issue. It is the transferring of data to newer system environments and the process of transferring information from one generation computer system to the next available computer generation that is advanced in nature. It also deals with the process of transferring information from one obsolete file format to a new standard file format. This may include conversion of resources from one file format to another (e.g. conversion of Microsoft Word to PDF or Open Document), from one operating system to another (e.g., Windows to Linux) or from one programming language to another (e.g., C to Java) so that the resources remain fully accessible and functional. Resources that are migrated face the risk of losing some type of functionality since newer formats may be incapable of capturing all the functionality of the original format, or the converter itself may be unable to interpret all the functionality of the original format. The latter is often a concern with proprietary data formats.
f) Emulation: Emulation uses emulator, a special kind of software that translates code and instructions from one computing environment (original obsolete software) to execute in a new platform so that the digital form can be viewed and used.
Emulation is the replicating of functionality of an obsolete system. Examples include emulating an Atari 2600 on a Windows system or emulating WordPerfect 1.0 on a Macintosh. Emulators may be built for applications, operating systems, or hardware platforms. Emulation has been a popular strategy for retaining the functionality of old video game systems, such as with the MAME project.
g) Metadata Attachment: Metadata is data on a digital file that includes information on creation, access rights, restrictions, preservation history, and rights management. Metadata attached to digital files may be affected by file format obsolescence. ASCII is considered to be the most durable format for metadata because it is widespread, backwards compatible when used with Unicode, and utilizes human-readable character, not numeric codes. It retains information, but not the structure information it is presented in. For higher functionality, Standard Generalized Markup Language (SGML) or Extensible Markup Language (XML) should be used. Both markup languages are stored in ASCII format, but contain tags that denote structured format. The long term storage of digital information is assisted by the inclusion of preservation metadata.
h) Analogue Backups: It is the process of the conversion of digital objects into analogue format. It is useful to the document that deserves the highest level of merit and protection from being lost. The analogue backup of printed document can be created by taking a printout of the document and then binding it.
i) Technology Preservation (Computer Museum): It deals with the preservation of the technology in which the digital information was created and maintained. It deals with the issues of preserving the technology including hardware and software configuration. It is very helpful in extending access to media obsolescence and file formats.
j) Digital Archaeology: Digital archaeology includes methods and procedures to rescue the content from damaged media, hardware or software environments.