In few older versions of Windows (Ex: Windows 3.0, 95, NT), the operating system installation disk was not bootable. In such a case, the installation would begin with a single startup disk or a set of installation diskettes. After loading the first set of required files the system will provide the user with a list of options; boot with CD-ROM support will be one of the options. On selecting it the system would load the required device drivers from the floppy. Two device drivers are needed for CD driver one is vendor specific, provided by the drive manufacturer and the other is a common driver provided by Microsoft. The driver provided by the Vendor is loaded to the CONFIG.SYS system file.
Microsoft MS-DOS & Windows 3.0 uses MSCDEX.EXE device driver file to access the CD-ROM drive. This file would enable DOS to access the CD-ROM drive as it would access to a floppy or a Hard disk drive. The file is loaded to the AUTOEXEC.BAT system file.
Almost all the operating systems available today come with a bootable operating system DISK. Apart from providing installation services these disk provide diagnostic modes and tools to troubleshoot and resolve common errors.
