The physical format of DICOM CD-R discs shall comply with the applicable definitions within ISO/IEC 10149, Part II: CD-WO in Orange Book and CD-ROM-XA (extended Architecture) (if Mode 1 sectors are not used), with the additional modifications described in sections F.2.1.1 and F.2.1.2.
All DICOM files and all data that comprise the ISO 9660 file system of the DICOM CD-R disc shall be stored either:
within Mode 1 sectors, or
within Mode 2, Form 1 sectors with CD-ROM-XA File Number = 0, Channel Number = 0 and Coding Information Byte = 0.
Notes: 1.The physical storage capacity of a CD-R disc can be 74 minutes (630 MB) or 80 minutes (700 MB) when using the Mode 1 or Mode 2 Form 1 format. The capacity is fixed by the pregrooved spiral track present on a blank CD-R. Some older CD players will not be able to read the 80 min capacity CD-R discs.
2. The DICOM standard prohibits the use of Mode 2 Form 2 sectors. This format is used to record data on CD-Rs that exceed 74 minute capacity and can also be used for smaller capacity CD-Rs. CD-ROM-XA Mode 2 Form 2 sectors do not have sector level error correction. This significantly decreases the reliability of the media and significantly increases the likelihood of data corruption.
An area on the disc consisting of a Lead-In area, a Program area, and a Lead-Out area, is called a "Session." If a disc contains or is able to contain more than one session then this disc is called a "Multi-session" disk. If the Lead-In area contains a pointer to the next session, then the disc is appendable. The Lead-In and Lead-Out areas are written at the conclusion of writing the program Area. The process of writing the Lead-In and Lead-Out areas is commonly referred to as "Finalizing the Session." The last recorded session contains all the information needed to access the entire disc.
DICOM CD-R disc may contain multiple sessions. Data are added to a disc by opening and writing a new session. A disc is non-appendable if the last recorded session is designated as the "Final Session," as defined in Part II: CD-WO version 2.0, Section 5.5.2.
CD-ROM readers shall support Multi-session CDs.
CD-R writers may choose to support Multi-session writing.