Microsoft MS-DOS 6.22 (6.22.2220) Upgrade 
Released 5/9/1994 by Microsoft
For IBM PC compatibles

MS-DOS 6.22 beta build 2220 from 9th May 1994. Upgrade version, so install
MS-DOS 5.0/6.0/6.20 first and then run SETUP.EXE from disk 1.