Setup Error Message Incorrectly Refers to IOSYS.HDR (114397)
The information in this article applies to:
• Microsoft MS-DOS operating system 6.21
• Microsoft MS-DOS operating system 6.22
This article was previously published under Q114397
If MS-DOS 6.21 or 6.22 Upgrade Setup cannot find the files IOSYSA.HDR or
IOSYSB.HDR, Setup displays the following error message:
Although the error message is correct in that Setup cannot find a required
file, it refers to a nonexistent file (IOSYS.HDR). The actual file Setup
cannot find is either IOSYSA.HDR or IOSYSB.HDR.
Microsoft has confirmed this to be a problem in MS-DOS 6.21 and 6.22 Setup.
We will post new information here in the Microsoft Knowledge Base as it
To correct this problem, ensure IOSYSA.HDR and IOSYSB.HDR are in the same
directory as SETUP.EXE.
IOSYSA.HDR and IOSYSB.HDR contain the checksum and size information for the
existing IO.SYS file. It provides a means for MS-DOS Setup to verify the
version and integrity of the existing IO.SYS file.
Each .HDR file can hold two different checksum/size pairs. IOSYS.HDR (from
MS-DOS 6.2 Step-Up) contains this information for the MS-DOS 6.0 and the MS-
DOS 6.2 IO.SYS files. MS-DOS 6.21 has to store information for more IO.SYS
files so both IOSYSA.HDR and IOSYSB.HDR are used. IOSYSA.HDR holds
information for the MS-DOS 6.0 and 6.2 IO.SYS files and IOSYSB.HDR holds
information for the MS-DOS 6.21 IO.SYS files. MS-DOS 6.22 IOSYSB.HDR holds
information for the MS-DOS 6.21 and 6.22 IO.SYS files.
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