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Minidisc is a magneto-optical memory device, released by Sony in 1992. The last Minidisc recorders were sold in 2013.

There were both pre-recorded discs and rewritable discs. The pre-recorded discs were popular only in Japan.

The duration is 60, 74 or 80 minutes. The disc size is
68 × 72 × 5 mm and the capacity is 140 MB, sample rate 44.1 kHz. Minidisc uses lossy ATRAC data reduction. A short output buffer prevents pauses in the playback. The playback is very robust against vibration.

A Minidisc Data version was released later and also a Hi-MD with a 1 GB capacity. These formats were not a success. The data version was used in some four- and eight-track music recorders.

Copying the disc contents

The Minidiscs are copied as a data transfer, which is much faster than playing and recording the disc in real time. The disc title and the written track names are also copied, and there is no need for any further editing.

Recovering accidentally lost and deleted tracks

The Minidisc's weak spot is saving the Table Of Contents. The TOC must be saved before the power is switched off in the same way as with floppy discs or CD-R:s. When the playback is started, the player looks for the information about the disc contents. If it doesn't find it, you are in trouble.

If the power is shut down, or if it accidentally cuts out before the TOC is saved (or even worse; during the saving) the TOC often gets corrupted. Many recorders do an automatic save, if the battery voltage drops too low, or if the user tries to eject the disc without saving the TOC.

Luckily the data still remains on the disc and it can be recovered. I have succesfully recovered several "lost" Minidisc recordings. It is also possible to recover such tracks that were intentionally deleted from the TOC, in case they haven't been recorded over.