RealSky is composed of the "RealSky" product, covering the northern sky, and "RealSky South," published slightly later and covering the southern sky. RealSky is on nine CD-ROMs (eight data discs and one software disc), and RealSky South uses 11 CD-ROMs (ten data discs and one software disc).
DSS files were compressed by a factor of 7, but RealSky files are compressed by a factor of roughly 100. RealSky consequently takes up less space, but the additional compression makes it inappropriate for use in photometry, and fine detail in the images is degraded.
The DSS covers the whole sky in two colors, red and blue; but RealSky provides only red coverage of the northern hemisphere while RealSky South provides only blue coverage of the southern hemisphere.
The DSS includes both long and short exposures for the area around the Andromeda Galaxy, but RealSky provides only the short exposure plate.