This article was previously published under Q74589
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The Microsoft MS-DOS Upgrade Setup copies the hidden system files IO.SYSand MSDOS.SYS to the front of the root directory in the boot drive. If theprevious version of DOS had files called IO.SYS and MSDOS.SYS created byMicrosoft, those files will be deleted.
If the previous version of DOS has hidden system files by other namesor that were not created by Microsoft, they are moved to the firstavailable 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, thehidden file attribute, and the read-only file attribute of a filenamed IBMBIO.COM.
attrib -s -h -r ibmbio.com
These files can also be deleted using MS-DOS Shell.