While they really aren't that old, MiniDiscs really don't have that much of a use now. They were probably invented because they're much more compact in size and easier to carry than the compact disc (CD).
The MiniDisc was invented in September 1992 by Sony. It is a magneto-optical disc-based data storage device for 74 minutes, and later, 80 minutes, of digitized audio of 1 gigabyte of Hi-MD data. While they enjoyed popularity in Japan, they made limited impact elsewhere and so Sony announced they would cease the development of MiniDisc (MD) devices last March 2013.One easy way to think about a mini disc is like a floppy disk - you can record and erase files on a mini disc just as easily as you can on a floppy disk. The big difference between the two is that a mini disc can hold about 100 times more data. They come in two forms - pre-recorded; and black and recordable.
While compact discs are still very much used by musicians for their music, the MiniDisc didn't gain the impact Sony wanted it to have. This is presumably because when Sony intended it for teenagers, the price wasn't teenager-procket friendly at all, with the MD player/recording costing $750 in 1992.
And then it was killed by the introduction of the MP3 player...More on this next week!
Edit: Changed photo as photo used before was of a mini CD not MiniDisc.