What is "hi-md"

In January 2004, Sony announced the Hi-MD media storage format as a further development of the MiniDisc format. With its release in later 2004, came the ability to use newly developed, high-capacity 1 gigabyte Hi-MD discs, sporting the same dimensions as regular MiniDiscs. The Hi-MD format can be considered obsolete as the last recorder/player was discontinued in 2011. The discs themselves were withdrawn from sale in September 2012, though regular MiniDiscs are still available .