The cartridge format used by the PlayStation Portable was the Universal Media Disc, or UMD.
Despite being commonly called a cartridge in casual conversation, UMD was an optical-disc format developed by Sony specifically for the PSP. The disc was enclosed in a protective plastic shell, giving it a distinctive small-disc appearance while helping shield the media from scratches and fingerprints.
UMDs stored PSP games, but Sony also released films, television programs, and music on the format. A single-layer disc held about 900 MB, while a dual-layer UMD could hold up to 1.8 GB. The PSP read the discs with a red 660-nanometre laser.
UMD's proprietary design limited its use to the PSP family. It had no widely available blank media or consumer writers, and the PSP Go later abandoned the format entirely in favour of digital downloads. The PlayStation Vita, PSP's successor, used flash-based game cards instead of UMDs.