4/2/2023 0 Comments Basilisk ii bin cue![]() ISO9660 is the most common format for carrying data on CD-ROMs, often appearing as the baseline filesystem on cross-platform discs. ![]() ![]() Methods of handling discs with open sessions are documented by the digital forensic community, due to their importance in evidence collection.įor purposes of this article, the structure of DVD is sufficiently similar to CD-ROM that it does not merit in-depth analysis. A session can have new tracks written to it so long as it is marked as open by closing it, it prevents further data from being added and creates the final table of contents. It merits noting that, on CD-R and CD-RW, a session can be open or closed. One session, one data track, many audio tracks (video game) Two sessions, one with many audio tracks, one with one track and many filesystems (Enhanced CD) One session, one track, many filesystems (typical data CD) One session, many audio tracks (typical audio CD) A diagram of the logical structure of a multi-session CD.ĭue to the flexibility of how data can be arranged on sessions and tracks, the following example configurations are possible: Early CDs were designed as if only one session would be on a disc this was expanded in 1990 to provide for multiple sessions.įigure 1. These tracks are arranged in a linear series and bounded by a lead-in (which contains the table of contents – locational and descriptive metadata – for the following tracks) and a lead-out. CD-ROM), any number of filesystems may be contained within a single track. A track is, as its name implies, designed to be one discrete track of audio. Hence, while it seems strange to discuss file-based data in terms of logical tracks, this is precisely how data is stored on CD-ROM.Ī simplified model of a compact disc’s logical structure is as such: a series of sessions, each containing a series of tracks. Thus, despite standards such as ISO/IEC 10149 (available as ECMA-130) providing for filesystem-based storage, the language and structure of Red Book persists. As the first optical media standard was IEC 60908 (1982) for audio storage and playback, future standards reflected a media-centric approach in how they structure the disc. It is crucial to understand the logical layout of optical media before attempting any preservation activities. This document, while offering recommendations, is also not a prescriptive cookbook of workflows and tools for dealing with optical media, as the necessary research for such recommendations has yet to be performed. Archivists dealing with such discs are recommended to explore more specialized resources, such as technical communities and standards documentation. The total forms and functions of optical media are many and varied – from analog video to hidden data to graphics stored in control codes – and are beyond the scope of this document. Note that this article deliberately limits its scope to the most common formats and uses of optical media. The author also hopes that, by providing a general overview of optical media preservation, more advanced conversations and explorations of the medium can take place. In doing so, it hopes to inform institutions working with such media as to the nature and challenge of optical media with regards to preservation. This document will cover five of the most common data storage standards for optical media. While a comprehensive account of all migration and preservation issues of optically stored data is impossible, there is a need for a broad overview of optical media, which this document hopes to provide. Given how recently archives have approached optical media as an object of preservation, there is little literature and research regarding the format. One collection of data CD-Rs from the 1990s yielded a 92% failure rate after approximately twenty years of storage. While longevity models estimated a lifespan of 25-200 years for recordable media, recent testing has found this range to be optimistic by orders of magnitude. The role of optical media in archives has shifted in the past decade from preservation medium to at-risk format. ![]()
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