IO.SYS

IO.SYS is a system file in the operating systems MS- DOS, Windows 9x and DCP. On IBM PC DOS and DR DOS so the corresponding file IBMBIO.COM. FreeDOS this functionality is provided by a file that usually bears the name KERNEL.SYS. IO.SYS is a part of the kernel and is required for booting the operating system. It is a file that is not writable and displayed in the normal case, because it is "hidden" or invisible. Together with MSDOS.SYS (MS -DOS), it forms the core component of the operating system DOS. For IBM PC DOS and DR DOS are the corresponding DOS files IBMBIO.COM and IBMDOS.SYS. In principle, rich these two files and a loaded program as COMMAND.COM in order to have a fully functional DOS, if one wishes to stop drivers, such as a mouse, keyboard layout, or CD -ROM driver.

The setup of Windows 9x extracted among other winboot.sys from the Cabinet archives on the installation media and rename this file to the end of the process in IO.SYS.

During the boot process, the boot sector is read and executed by the boot disk into memory. The DOS boot sector loads the first three sectors of IO.SYS file / IBMBIO.COM. At this time, the driver for the FAT file system is not loaded yet, so first of all, secondly unfragmented this file at the beginning of the data area of the disk and, third, the first file must be in the root directory. From DOS 4.0, the file may be fragmented except for the first three sectors. With DOS 5.0, the file must be stored on any place of the disk, which here must be the first three sectors contiguous (not fragmented); the relevant information is stored in the boot sector.

After the first three sectors of the file are read and executed, the rest of the file is read and it carries out the following steps:

• There are standard device drivers loaded and made available
• The DOS kernel MSDOS.SYS ( IBM: IBMDOS.COM ) is loaded and initialized ( in Windows 9x is this integrated into IO.SYS ). From this point, the file system driver is loaded, and the normal disk access is guaranteed.
• In Windows 9x, the configuration file ( winboot.ini or MSDOS.SYS ) of the DOS kernel is processed. Does this in the Options section no entry " BootMulti = 0" and are the relevant system files to a previous version of DOS (MS- DOS, PC -DOS 5 or 6) present, and the old system be started ( " dual boot " option ). When you select this option, the first relevant current DOS files are renamed by the file extension is replaced by W40. An exception is the IO.SYS file that is renamed to Jo.sys. Then the old DOS system files obtained with the DOS file extension back to its original name, the old DOS kernel is loaded and the processing is resumed as described above.
• The CONFIG.SYS file is processed ( since DOS 2.0) except in "safe mode ". During the boot process, indicated by a message such as " Starting Windows 95 ", can usually be changed directly in this mode by pressing the F5 function key. Or, from the Start menu, which typically appears when you press F8, you can select this mode. He is also started when MSDOS.SYS in the Options section contains the entry " BootSafe = 1".
• If in CONFIG.SYS no other command line interpreter or other executable program has been defined by shell directive, is the COMMAND.COM file located in the root directory, started and thus loaded the MS -DOS command line interpreter. This then usually leads from AUTOEXEC.BAT.
• Normally when you start Windows 9x, a startup logo is displayed if it is not prevented by the entry " Logo = 0" in the configuration file. IO.SYS generated this with the graph file LOGO.SYS. If this is so the logo contained in IO.SYS used.