DOS or Disk Operating System; is related to different operating systems. Earlier IBM was on the top of the list during 1981 to 1995 and then came Windows which included Open DOS, MS DOS, PC DOS and some more. The main attraction which these operators had was that only a single user can use this and it can perform only one task at one time. One out of the list was MS DOS which was from Microsoft originally, was used in a huge manner. The compatibility of this operating system differs, as they can be operated on IBM PC hardware and having different configurations. Later, MS DOS was considered to be the foundation stone for the other operating systems.

During the days when use of the micro computer was at boom and the main constraint was the size of the memory. That time the DOS was introduced as an addition to the operating system. Only the lower level processes as writing or reading something. Earlier the programs were not functioning on a large scale but later on there were many changes and the system was much advanced. The reason behind considering DOS as the pioneer of the operating system was its existence for long time in the threshold of the compatible PC. Different versions are there of DOS, namely Open DOS and Free DOS. Out of these two Free DOS was started around the year 1994; as there was difference between Windows 95 and Windows 3.11 without any provision.

By July 1981, exclusive rights for 86DOS were declared and it was renamed as MS-DOS. The first IBM version was released in August 1981. Later on different versions of MS DOS were introduced. A special software is required to handle the continuous usage of the data and importantly the system is used by the hard disks and the floppy disks been used. The disks were very much expensive earlier and during that time it was necessary to have such expensive software installed in the system for effective results.

Some of the device names are reserved and they are not to be used as the names of the files. The same kinds of constraints are for other forms of Windows as well; due to which sometimes the system also fails sometimes and it may cause some kind of problems in the system.