MS-DOS 6.22 Missing Boot File Error Messages

When MS-DOS 6.22 fails to start due to missing boot files, the exact error message displayed depends on which stage of the boot process fails and which specific file is missing. The operating system relies on three critical files to complete startup: IO.SYS, MSDOS.SYS, and COMMAND.COM. Missing these components typically produces either the "Non-System disk or disk error" prompt or the "Bad or missing Command Interpreter" notification.

Missing IO.SYS or MSDOS.SYS

If the master boot record or partition boot sector cannot locate the core system files (IO.SYS and MSDOS.SYS) in the root directory of the boot drive, the bootloader halts and displays:

Non-System disk or disk error
Replace and strike any key when ready

This error commonly occurs if:

  • A non-bootable floppy disk is left inside drive A:.
  • The hard disk was formatted without system files (omitting the /S parameter during formatting).
  • The hidden system attributes on IO.SYS or MSDOS.SYS were modified or the files were accidentally deleted.

Missing COMMAND.COM

If IO.SYS and MSDOS.SYS load successfully, but the primary shell program COMMAND.COM cannot be found in the root directory or at the location defined by the SHELL= statement in CONFIG.SYS, the system halts with:

Bad or missing Command Interpreter
Enter correct name of Command Interpreter (eg, C:\COMMAND.COM)

At this prompt, MS-DOS pauses and awaits keyboard input pointing to a valid copy of the command interpreter. If the file cannot be supplied, the operating system cannot load the command-line interface, preventing normal operation.

Resolution

To resolve these errors, boot the computer using an MS-DOS 6.22 setup or emergency boot diskette, then restore the files using the following methods:

  • For missing system files: Run SYS C: from the floppy drive to transfer clean copies of IO.SYS and MSDOS.SYS along with COMMAND.COM directly to the hard drive.
  • For a missing command interpreter: Manually copy COMMAND.COM from the boot floppy to the root of the target drive using COPY A:\COMMAND.COM C:\.