INT 21h, 5D00h    Indirect function call
 INT 21h, 5D01h    Partly unknown - updates System File Table
 INT 21h, 5D02h    DOS 3.1 internal - SHARE.EXE ??
 INT 21h, 5D03h    DOS 3.1 internal - SHARE.EXE ??
 INT 21h, 5D04h    DOS 3.1 internal - SHARE.EXE ??
 INT 21h, 5D05h    DOS 3.1 internal - SHARE.EXE ??
 INT 21h, 5D06h  Get address of critical error flag
 INT 21h, 5D08h  ??? (used by COMMAND.COM)
 INT 21h, 5D09h  ??? (used by COMMAND.COM)
 INT 21h, 5D0Ah  Set Extended error information