A standard single-sided, dual-layer Universal Media Disc could store up to 1.8 GB.
Sony created the Universal Media Disc, or UMD, specifically for the PlayStation Portable. Its small optical format was used for PSP games, films, and some other media releases. The disc was enclosed in a protective plastic cartridge-like shell.
The 1.8 GB figure describes the maximum capacity of a dual-layer UMD. UMDs were optical discs, so their capacity should not be confused with the removable Memory Stick storage used for saves, downloads, and other files.
Some references describe UMD capacity as approximately 1.8 gigabytes rather than presenting the figure as a rounded marketing number. The format was proprietary to Sony and was not used by the company’s later PlayStation Vita handheld.