SUMMARY

The Microsoft MS-DOS Upgrade Setup copies the hidden system files IO.SYS and MSDOS.SYS to the front of the root directory in the boot drive. If the previous version of DOS had files called IO.SYS and MSDOS.SYS created by Microsoft, those files will be deleted.

If the previous version of DOS has hidden system files by other names or that were not created by Microsoft, they are moved to the first available space in the root directory of the bootable hard drive. These files can then be deleted after resetting the file attributes.

The following command will turn off the system file attribute, the hidden file attribute, and the read-only file attribute of a file named IBMBIO.COM. These files can also be deleted using MS-DOS Shell.