IO.SYS

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IO.SYS is a system file in the MS-DOS , DCP and Windows 9x operating systems . Under IBM PC DOS and DR DOS the corresponding file is called IBMBIO.COM . With FreeDOS , this functionality is provided by a file that usually bears the name . is part of the kernel and is required to boot the operating system. It is a file that is normally write-protected and not displayed because it is invisible or " hidden ". Together with (MS-DOS) it forms the core component of the DOS operating system. For IBM PC DOS and DR DOS, the corresponding DOS files are and . In principle, these two files and a loaded program are sufficient to have a functional DOS, provided that additional drivers such as mouse, keyboard layout or CD-ROM drivers are dispensed with. KERNEL.SYSIO.SYSMSDOS.SYSIBMBIO.COMIBMDOS.SYSCOMMAND.COM

The Windows 9x setup extracts WINBOOT.SYS from the cabinet archives on the installation medium and renames this file towards the end of the process IO.SYS.

During the boot process, the boot sector is read into memory from the boot medium and executed. The DOS boot sector loads the first three sectors of the file IO.SYS/ IBMBIO.COM. At this point in time, the driver for the FAT file system has not yet been loaded, which means that this file must firstly be at the beginning of the data area of ​​the data carrier, secondly unfragmented and thirdly be the first file in the main directory. As of DOS 4.0, the file may be fragmented except for the first three sectors. With DOS 5.0, the file can be stored on any location on the data carrier, whereby the first three sectors must also be contiguous (not fragmented); the corresponding information is stored in the boot sector.

After the first three sectors of the file have been read and executed, the rest of the file is read and the following steps are carried out:

  • standard device drivers are loaded and made available
  • the DOS kernel MSDOS.SYS(at IBM:) IBMDOS.COMis loaded and initialized (this is IO.SYSintegrated in Windows 9x ). From this point on, the file system driver is loaded and normal data carrier access is guaranteed.
  • With Windows 9x, the configuration file ( WINBOOT.INI or MSDOS.SYS) of the DOS kernel is processed.If this Optionsdoes not contain an entry in the section BootMulti=0and the relevant system files from a previous DOS version (MS-DOS, PC-DOS 5 or 6) are available, the old system can also be started (“dual boot” option). If this option is selected, the current relevant DOS files are first renamed by replacing the file extension with W40. An exception is the file IO.SYSthat is assigned to WINBOOT.SYS(Windows 95) /JO.SYS(Windows 98 / ME) is renamed. The old DOS system files with the file extension are DOSthen given their original names again, the old DOS kernel is loaded and processing is resumed as described above.
  • the CONFIG.SYSfile is processed (from DOS 2.0) except in" Safe Mode ". During the boot process, recognizable by a message such as "Windows 95 is starting", you can normally switch directly to this mode by pressing the F5 function key. Or this mode can be selected in the start menu, which typically appears when you press F8. It is also started if it contains the entry MSDOS.SYSin the Optionssection BootSafe=1.
  • If no other command line interpreter or another executable program has shellbeen defined in CONFIG.SYS via directive, the COMMAND.COMfile in the main directory is started and the MS-DOS command line interpreter is loaded. This then normally executes AUTOEXEC.BAT.
  • A start logo is normally displayed when Windows 9x is started, if this is not prevented by the entry Logo=0 in the configuration file. IO.SYSgenerates this based on the graphic fileLOGO.SYS. If this is missing, the logo contained in IO.SYS is used.

Web links

literature

  • Harald Milz: The interrupt 21h during the DOS boot process In: ct 7/1992, p. 198ff.
  • Peter Siering: Windows 95: old DOS for new Windows In: ct 5/1996, p. 284

Individual evidence

  1. ↑ support.microsoft.com
  2. ↑ support.microsoft.com
  3. ↑ support.microsoft.com
  4. ↑ support.microsoft.com
  5. ↑ support.microsoft.com
  6. ↑ Klaus Dembowski: BIOS and Troubleshooting: compact, complete, competent . Markt + Technik], Munich 2004, ISBN 3-8272-6547-9 , p. 36 .
  7. ↑ support.microsoft.com
  8. ↑ support.microsoft.com