Operating Systems and their File Systems

DOS - MS-DOS^®- PC-DOS^®

If you have been involved with computers and their operating systems for any length of time, since maybe 1995 or so, then you probably recognize the abbreviation "DOS". The first operating system used on the earliest of the IBM small computers was referred to as the Disk Operating System, hence the abbreviation. If you're a rather recent computer user, then you may not recognize DOS at all. At one time DOS was used on nearly every small computer in production. This may change though as the industry transitions from DOS based operating systems to more popular operating systems such as Windows^® and Linux^®. Although DOS is still around today in varying forms, Microsoft's version of DOS is the most common, referred to as MS-DOS^®, which was originally developed in 1981. For a relatively short period of time, the IBM Corporation was producing a competing product referred to as PC-DOS^®, and there are other forms of DOS available, such as DR-DOS^®. Instead of getting into the nuances of each and every version of DOS from all of the various developers, we're going to stay with IBM's DOS, MS-DOS^® and where necessary, PC-DOS^®.

As the name implies, the integral part of the DOS operating system are disks. The FAT file system has been an essential component of DOS from the very beginning. It uses various versions of FAT for managing files, and each version of FAT is supported by its own version of DOS, as follows:

• DOS 1.x and 2.x: This version of DOS supports only the FAT 12 file system, which is primarily used today for floppy disks.
  
  
• DOS 3.x through 6.x: DOS versions 3.x through 6.x are the most common versions found on older legacy computers that are (were) running either DOS only or Windows^® 3.x. Versions 5.x and 6.x were the most popular versions, with millions upon millions of copies having been sold. Versions 3.x through 6.x support FAT 12 as well as FAT 16, with FAT 16 becoming the file system standard as it is today.
  
  
• DOS 7.0: MS-DOS^® version 6.22 was the last standalone version sold by Microsoft. After version 6.22, all other versions were sold as the foundation (of sorts) of other operating systems, such as Windows^® 9x/ME. The first of these was MS-DOS 7.0, which ran underneath the first Windows^® 95 version (95A). It supported FAT 12, FAT 16 and VFAT, the enhanced version of FAT that included support for long file names. Although Microsoft made every effort to convince users that Windows^® ME was free of MS-DOS^®, in truth it was not.
  
  
• DOS 7.1 and later: These versions were the foundation for Windows^® 95 versions beginning with Windows^® 95 OEM Service Release 2 (Windows 95B) and later. These versions continued to support FAT 12, FAT 16, VFAT as well as FAT 32.

When FAT 32 support made its first appearance in the second release of Windows^® 95 there was considerable confusion on the part of users, made worse by the fact that later versions of Windows^® that supported FAT 32 were not officially sold to the general public. As we discuss Microsoft's Windows 95 versions, A, 95B and 95C, we'll cover this issue more in depth. If you recall Microsoft's advertising surrounding the last release of Windows^® 98 and then Windows ME, you'll see that they desperately wanted people to believe that Windows^® 98 and Windows^® ME did not run on an old DOS platform.

Choose a platform from the list below to advance this discussion.

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