MS-DOS is text based operating system, which can be installed. with windows
MS-DOS and Windows XP:
MS-DOS must be installed on a basic disk on a partition formatted with FAT. If MS-DOS is not installed on the system partition, which is almost always the first partition on the disk, the system partition must also be formatted with FAT.
Windows XP must be installed last. Otherwise important files needed for starting Windows XP could be overwritten.
DOS:
DOS is quite simple to describe, since it principally consists of only 4 parts
# A boot record, which activates the operating system.
# The file IO.SYS, which is interfaced to ROM BIOS with installation of device drivers .
# The file MSDOS.SYS. That is the core of DOS, handling the file system and program execution.
# The file COMMAND.COM, which provides the command line, the text based user interface.
When we talk about hardware control, it is done through IO.SYS. That is a program which reads the ROM BIOS code and converts it to DOS's own device drivers.
The smart thing about DOS is that the operating system can be expanded with external device drivers. IO.SYS reads them via the start-up file CONFIG.SYS. First device drivers are read from ROM BIOS. Then any possible additional drivers are read from disk. In that way DOS can handle hardware units which did not exist when the PC was originally configured.