The evaluation process should fully take into account variations within a media type. For example, a number of different dye and metal layer combinations are available for CD-Rs. In this example, CD-Rs with a gold reflective layer and phthalocyanine-based dyes have been assessed, since recent research suggests that these are the most stable, and have the greatest life span. In situations where multiple copies of data are stored on separate media, it may be advantageous to use different media types for each copy, preferably using different base technologies (for example, magnetic and optical). This reduces the overall.
