DICOM specifies a standard for storing images and other composite objects on media such as a CD or DVD for the purpose of exchange. Application profiles are used to specify this for particular applications such as CT/MR, US, cardiology and general purpose use.
The DICOM standard is primarily a communication standard. There is no explicit definition of a DICOM archive and/or how or with what format the DICOM objects should be archived or stored. An archive is purely a device that supports one or more of the DICOM services such as storage or query/retrieve with no internal data representation.
However, DICOM standardizes the storage of images and other DICOM objects on removable media such as CDs or DVDs for non-network exchange. As with a DICOM communication exchange, where each device can either play the role of a SCU or SCP, or both, for media support a device can claim different roles: File Set Reader (FSR), when it can read the exchange media, FSC, when being able to create or write the media, or FSU, when it can update the directory.
There are several applications for these. One could, for example, store the images on a CD and give it to a patient so he or she can take it to the physician for a follow-up treatment. Rather than providing a film or even paper, it is easier and less expensive to do it that way.
Another application would be to accumulate images on media for temporary storage. Imagine a portable Ultrasound unit that is acquiring images off-line. When storing the images temporarily on a disc, they can easily be downloaded and read into a workstation for review. Because of the frequent rewrite, these devices often use the more robust MOD instead of CD or DVD.