Optical media were first created by researchers in the 1960s but became widely known with the commercial production of audio-formatted CDs (Compact Disc Digital Audio, or CDDA) and CD-ROMsin the 1980s. The DVD (Digital Versatile Disc) became popular in the late 1990s and was used to store video as well as data. Optical disk writing technology led CDs and DVDs to become ubiquitous storage devices from the 1990s through the 2010s. A standard CD can hold approximately 700 MB while a single-sided DVD can hold 4.3 GB.
Identifying Different Types of Optical Media
Proper identification of optical media is essential for the successful recovery of data in the BDPL Ingest Tool workflow. While it is often possible to distinguish a CD from a DVD by manufacturing marks, it will be necessary to examine discs in the Windows File Manager to determine if a disc is for data or is formatted for audio or video. Go to 'This PC' in the Windows File Manager to view the disc's icon and open the disc to examine its contents.
Data DVDs and CDs
Data CDs and DVDs have files (and possibly folders) burned onto a file system, and may include a wide variety of file formats, including audio and video files (such as MP3 or MOV). Under 'This PC', Windows will typically identify a data disk with icons bearing labels such as 'CD-ROM', 'CD-R', 'DVD-ROM', 'DVD+R', etc.:
In addition, if you right-click on one of these icons and select 'Open', you will find that the disc contains folders and/or files:
Compact Disc Digital Audio (CDDA)
A CDDA disk has been specially formatted to meet the specifications of the IEC 60908 standard and contains two-channel signed16-bit Linear PCM (Pulse-Code Modulated) audio sampled at a rate of 44,100 Hz/sec. In the Windows File Manager, a CDDA disc typcially has an icon with a music note and will also include the letters 'CDFS' (for Compact Disc File System):
When opened, an audio-formatted CDDA disc will include CD Audio shortcut files (note the '.cda' extension)–these are not the music files themselves, but instead serve as shortcuts to the different tracks on the audio disc:
NOTE: if the disc does not include these .cda 'files', it is not a CDDA disc.
A video-formatted DVD (or DVD-Video) is a consumer video format used to store one or more video titles that can be played in a DVD player or similar computer application. When viewed in the Windows File Manager, a DVD-Video disc will display an icon with the letters 'DVD':
When opened, a DVD-Video disc will display a VIDEO_TS folder (and in some cases, an AUDIO_TS folder); this directory structure will include a number of Video Manager (VMG) files as well as Video Title Set (VTS) files that will include .IFO, .BUP, and .VOB files.
NOTE: in some rare cases, the VIDEO_TS folder may be nested inside an additional top-level directory.
- Avoid fingerprints or smudges by touching only the center or edges of the disc.
- Do not write on discs with any solvent-based markers, ball-point pens, pencil, etc.
- Do not attach labels directly to discs because this could damage the disk, or cause an imbalance that could damage the player or drive. Instead, label the jewel case.
- Avoid scratches on EITHER side of the disc. For CD's the data is located just below the laquer layer, so the label side may be more vulnerable than the plastic side. DVD's are less vulnerable, since the data is located in the center layer of the disc.
- Magnets are not a concern for optical media.
- CD's that have absorbed a large quantity of moisture can become unreadable, but may work properly once they dry out.
- Avoid prolonged heat exposure, such as leaving discs in direct sunlight, or placing them on or near a hot CPU.
- Prolonged exposure to sunlight, or other sources of UV light, will cause the dye (recordable) layer in CD/DVD-R discs to break down significantly. Keep all discs out of the sun and away from UV light.
Use the built-in optical disc drives in the Windows workstations to transfer data off of optical media. BDPL staff have reported several instances where an optical disc failed to transfer in one drive, but succeeded in the other workstation; if a failed disc does not exhibit any obvious flaws or damage, be sure to try it in another workstation.
Optical media should not require any additional write-protection, as commercially-produced and recordable discs are automatically write-protected once they have been finalized or "burned."