DOS (Disk Operating System) was developed by the Microsoft Corporation, as the standard operating system for use with IBM personal computers. It controls the basic functions of the computer, and is especially handy for working with data stored on disks. The DOS system resides on diskette (3.5" or 5.25") and the system files may be transferred to a hard disk unit.
An operating system is a program that allows competing programs to share the resources of the computer (memory, disk, and devices like printers and modems, and processing time). The operating systems first job is to initialize the hardware of the computer system, before running application programs. For personal computers, MSDOS is a single user, single tasking operating system. Single user means only one person uses the computer at a time. Single tasking means that it essentially only runs one application program at a time, and has no inherent support for running more than one application program simultaneously. An operating system provides mechanisms for running programs, handling errors, controlling devices, configuring the computer system, and for MSDOS, a user interface (sometimes called a shell).

The main system part of MSDOS consists of three files:


IO.SYS implements MSDOS as seen by the hardware. It has default device drivers for

console display and keyboard
serial communications
boot disk drive

MSDOS.SYS implements MSDOS as seen by application programs. It supports

file and record management
memory management
character device input and output
execution of other programs
access to a real-time clock

COMMAND.COM is the shell program that interprets user commands, presents the shell prompt, and contains a set of internal commands. A diskette used to load MSDOS into the computer must contains these three files. In addition, these files must be first on the diskette.
The rest of MSDOS consists of utility programs. Examples of these are:

backup backup files to another disk
format format a disk for use by MSDOS
print print a file
restore restore a backed up file(s) from disk
xcopy copy a range of files and sub-directories
The hardware associated with your computer are devices. Examples are keyboards, mouse and video screen. For every device associated with your computer, MSDOS uses a program to control it. This program is called a device driver. MSDOS provides built-in device drivers for the keyboard, monitor and disk drives. These built-in
device drivers are automatically loaded by MSDOS and are an integral part of it. MSDOS supports installable device drivers. These are device drivers that support additional hardware added to the computer, and are loaded at boot time. Examples of installable device drivers are CDROM\'s, mice, plotters etc. When MSDOS boots, it looks for a file called config.sys in the root directory. This file specifies which device drivers to install and where they are found.