The creation of the MiniDisc MD
MiniDiscs were announced in 1991 by Sony as a disc based digital medium for recording and distributing consumer audio that is “near CD” in quality.
In 1993 Sony announced MD Data, a version of the MiniDisc for storing computer data.
There are two physically distinct types of discs: Pre-mastered MDs, similar to CDs in operation and manufacture, and Recordable MDs, which can be recorded on repeatedly and employ magneto-optical technology. The disc itself is enclosed in a small (7cm x 7cm), convenient, cartridge.
Nearly 160MB for 74 min. in audio mode [140MB in Data Mode]
What is the difference between the 60,74 and 80 min of MD?
The pregroove wobble is at a higher linear frequency (cycles/cm.) on the 74 minute blanks, causing the recorder to spin the disc slower (74 min: 1.2 m/s vs. 60 min: 1.4 m/s) and thereby record more information in the same linear space.
The 80 minute discs are made by decreasing the track pitch (i.e. space between tracks) from the MD standard’s 1.6um to 1.5um (micrometers), the minimum allowed by the MD specification; like the 74′ blanks, they also run at 1.2 m/s.
There is also information encoded in the read-only TOC near the inner circumference of the disc telling the player how long the disc is.