NSK-DOS

 (pronounced "next-doss") is a disk operating system released by Naisuka for their PCs between 1980 and 1996. Initally released in 1980 as a  clone, NSK-DOS switched into being a / compatible operating system. However, unlike other DOS-compatible operating systems at that time, NSK-DOS was never released as a standalone product and was only came bundled with Naisuka’s personal computers.

Versions

 * NSK-DOS 1.x (1980)
 * NSK-DOS 2.x (1981)
 * NSK-DOS 3.x (1983)
 * NSK-DOS 4.x (1985)
 * NSK-DOS 5.x (1987)
 * NSK-DOS 6.x (1990)
 * NSK-DOS 7.x (1993)
 * NSK-DOS 8.x (1994)