What is Disk Operating System (DOS)?

DOS stands for Disk Operating System. In general terms, DOS is a command line interface (CLI) OS to manage data in disks. This means that any OS that allows the user access and manage date in disks is a DOS whether that DOS is compatible with others or not.

What we have been accustomed to is DOS as the CLI OS for the IBM Personal Computer and clones written by Tim Paterson and then sold by Microsoft, on which Windows was later built on.

Although IBM originally used the same acronym in the early 1970s for their disk operating system for IBM System/360, the 1970s version of DOS (later replaced by VSE) is not the same as what we commonly know as DOS for IBM PC and clones.

In computer science, many terms are confusing and DOS is one of them. If it is spelled DoS (lower case `o`), we refer to denial of service. In this page, I am covering DOS (all upper case).

To make matters ever more confusing, one of the biggest misconceptions nowadays is that many think that DOS is MS-DOS (Microsoft's version of DOS).

MS-DOS (Microsoft)

In the early 1980s Microsoft bought the source code for 86-DOS (commonly referred to Quick and Dirty Operating System, QDOS), which was developed by Tim Paterson for the Intel 8086 microprocessor, for Seattle Computer Products (SCP). 86-DOS contained about 4,000 lines of assembler. QDOS later became PC DOS for the IBM Personal Computer system on August 1981. DOS was not developed originally by Microsoft and Bill Gates (in his book The Road Ahead, 1995) recognizes Tim Paterson as the father of DOS. Although Microsoft's version of DOS (MS-DOS) has become obsolete, many DOS clones and OS that can interpret DOS exist and are commonly used.

Nowadays, what is left of MS-DOS is reduced to a handful of files buried in C:\WINDOWS\COMMAND in Windows 9x, C:\WINNT\SYSTEM32 in Windows NT 4 or C:\WINDOWS\SYSTEM32 in Windows NT 5 (XP) and up — not to be confused with PowerShell (C:\WINDOWS\SYSTEM32\WINDOW~1\V1.0). I would like to see DOS included back in Windows as a stand-alone OS (similar to what macOS did with Unix). Worse of all, Windows NT 4 and up use an emulation of MS-DOS 5.0 (1991) — not 6.0 (1993) or 6.21/6.22 (1994) — that makes our life hell when trying to work with old DOS commands and batches. Some of these commands do not work anymore or exist anymore. Microsoft forces users to use the less effective Windows 4.xx versions of programs that were reliable in DOS.

MS-DOS as a stand-alone OS (less than 5 MB in MS-DOS 6.22) has not been marketed by Microsoft, since 1994. Microsoft opted to concentrate on the Windows graphical OS project in 1983 (marketed against Steve Jobs' Apple Macintosh, 1984).

DOS originally included BASIC, which later became QuickBASIC and then QBasic (QBASIC.EXE). Nowadays, Microsoft does not include any programming language by default. QBASIC.EXE has to be copied from D:\OTHER\OLDMSSDOS to C:\WINDOWS\COMMAND.

DOS Shell (230 KB) was last included in MS-DOS 6.2. Amazingly DOS Shell (PC DOS) was dropped around the same time.

The D:\OTHER\OLDMSSDOS (Old MS-DOS) directory on the Windows 95/98 disk has 17 files. Note that D: is your CD-ROM drive and that there is no TREE, just DELTREE. See directory below.

Windows 3.1 was the last version running as a system program running on MS-DOS. The latter is the foundation of Windows 4.x. Windows NT 4 and up are based on a different kernel and its CMD.EXE file merely emulates MS-DOS 5.0.

Maybe you can get your hands on any used copy of MS-DOS 5.0 (1991) or MS-DOS 6.22 (1994). Be careful since Microsoft might consider the latter activity illegal. You can download free of charge and use FreeDOS.

Installing MS-DOS on i386 & i486 Systems:

This technique is different from what most nowadays books indicate, using FAT16. The only drawback of installing FAT16 DOS is that the HDD has to be divided into partitions not larger than 2 GB each (seen by the system as separate disks). The first partition is primary and the rest are logical partitions.

You can also use a RAM drive (RAMDRIVE.SYS), which will increase memory performance similar to paging. Since it is not a physical disk, you should not save anything on it that you really want to save.

These instructions cover MS-DOS only although they might also apply to DOS clones. Reference to PC DOS 2000 is supplied. Unfortunately I do not have experience on other versions of DOS like DR-DOS 7.03 (only 3.13 MB, 3 floppies), which is differently and not normally taught in schools.

The installation procedure, explained in this site, is different from what most books might tell you. Both CONFIG.SYS and AUTOEXEC.BAT are changed. RAM is improved. By using this technique, a DOS and Windows set-up would work almost as well as /swap in Unix.

Run FDISK.EXE from the boot disk.

        
        A:\FDISK
      

View old partitions, if any, and delete them.

Delete first non-DOS partitions, then logical, then extended and finally the primary (if any).

Make primary partition. Since MS-DOS has a FAT16 architecture, MS-DOS cannot read more than 2 GB at a time.

Make secondary partitions (less than 2 GB). On the secondary partition, make logical partitions if needed. If the logical partition is close or over 2 GB, make 1 GB partitions. Then FORMAT each partition.

        
        A:\FORMAT C:
        A:\FORMAT D:
        A:\FORMAT E:
      

Install MS-DOS 6.22 or PC DOS 7 or 2000 on the HDD.

Make sure CONFIG.SYS recognizes as many logical partitions as you need. The total number cannot exceed 26 logical partitions (one for each letter of the English alphabet). Each partition will be assigned a letter by MS-DOS.

        
        LASTDRIVE=Z
      

Create backup files (.BAK) of CONFIG.SYS and AUTOEXEC.BAT before doing changes. Should there be a problem while booting, change CONFIG.BAK and AUTOEXEC.BAK back to CONFIG.SYS and AUTOEXEC.BAT accordingly. It is better to be safe than sorry.

Open CONFIG.SYS and AUTOEXEC.BAT with EDIT on MS-DOS or E on PC DOS. Then save them with the new names.

        
        C:\EDIT
        C:\E
      

You may also copy them to new files with different names, of course.

        
        COPY AUTOEXEC.BAT AUTOEXEC.BAK
        COPY CONFIG.SYS CONFIG.BAK
      

At this point, you can create the RAM drive (or virtual disk) that I mentioned before.

        
        DEVICEHIGH=C:\WINDOWS\RAMDRIVE.SYS 2048 /E
      

Do changes on CONFIG.SYS by adding the following lines to mount a CD-ROM in MS-DOS.

        
        DEVICEHIGH=PRE>C:\DOS\AOATAPI.SYS /D:IDECD000/Q
      

Then edit AUTOEXEC.BAT.

        
        LH=C:\DOS\MSCDEX.EXE /D:IDECD000
      

Copy AOATAPI.SYS to the HDD from MS-DOS. Both CONFIG.SYS and AUTOEXEC.BAT need this file, so copy it to your HDD.

        
        A:\COPY AOATAPI.SYS C:
      

Run MEMMAKER (MS-DOS 6.x) to optimize memory management in MS-DOS. PC DOS does not have MEMMAKER, but rather RAMBOOST, which does a similar job, including EMM386.EXE to simulate expanded memory.

Reboot system pressing F8, which will let you confirm each step of the CONFIG.SYS and AUTOEXEC.BAT. If there is a problem, reboot system pressing F5 bypassing CONFIG.SYS and AUTOEXEC.BAT. Change CONFIG.BAK and AUTOEXEC.BAK to CONFIG.SYS and AUTOEXEC.BAT. Repeat instructions or throw these instructions away. Either way, it is still a fun learning experience.

Make sure the BIOS will read CD-ROM first. Follow instructions provided by the computer manufacturer.

Reboot system with the Windows CD-ROM or 3.5 floppies. If you are installing Windows 3.1 on an i386 or i486 PC, check out the Calmira shell.

Depending on your needs, you might need to connect the system to a network (internet or LAN, most likely) or not. If you do, you need to load to memory the correct packet driver for the network interface card (NIC) on boot. Note that the packet driver is a .COM file ending on PD (for packet driver). Add the following line to AUTOEXEC.BAT replacing FOOBARPD.COM with the correct packet driver file name.

        
        LH FOOBARPD.COM 0X60 5 0X300
      

In the example above, the first parameter (0X60) sets the interrupt. The second one (5) sets the IRQ and the last one (0X300) sets the I/O port.

Maintaining a Hard Drive Running MS-DOS & Windows:

I have put together a batch file (set of organized commands), which will DEFRAG and SCANDISK your HDD. The batch is compatible with i386 clones with DOS like FreeDOS. Keep in mind that you can only run the batch in MS-DOS, not from Windows.

If you do not want to see the DOS commands while the batch file is running, edit the batch turning ECHO off.

        
        ECHO OFF
      

All files are randomly saved on your HDD. A practical way to manage your HDD would be having all parts that form a file together. DEFRAG organizes files fully (/F), defragments (defrags) files leaving space between them (/U), sorts them by extensions (/SE) and skips using extended or upper memory (/SKIPHIGH).

        
        DEFRAG /F/U/SE/SKIPHIGH C:
      

SCANDISK repairs problems that your all disks may have automatically without prompting (asking), deletes errors, skips summary and checks the surface the disk. This line of code might not work with other distributions of DOS.

        
        SCANDISK /ALL/AUTOFIX/NOSAVE/NOSUMMARY/SURFACE
      

The batch creates (if not already created) and assigns C:\TEMP as the temporary directory instead of using C:\DOS or C:\WINDOWS as a temporary directory. Some programs delete the temporary directories after installation. This would be serious trouble if the installation routine deleted the C:\DOS directory.

        
        IF NOT EXIST C:\TEMP MKDIR C:\TEMP
        TEMP=C:\TEMP
      

If you are running Microsoft Office 6.0 or earlier, you might want to delete all temporary files, which start with a tilde (~).

        
        DEL C:\~*.* /F/S/Q/A:R/A:H/A:S/A:A
      

Note that using the recursive switch (/S) in DEL tells the system to delete a certain criteria (in this example, ~*.*) in all subdirectories from a specific starting point, (in this example, C:, meaning the whole drive).

To delete any temporary files created by other programs, delete by force the contents of the C:\TEMP directory and all subdirectories without being prompted to confirm deletion, regardless of their attributes.

        
        DEL C:\TEMP\*.* /F/S/Q/A:R/A:H/A:S/A:A
      

If you want to generate a log of the deletions, send the output to text file (for this example, FOO.TXT). In the example below, the system will first write the date (%DATE%) and time (%TIME%) when the batch is run and two blank lines (ECHO., including the period after ECHO) after the log has been generated for cosmetic purposes. As such, these blank lines can be excluded.

        
        ECHO OFF
        ECHO %DATE% %TIME% > FOO.TXT
        DEL C:\~*.* /F/S/Q/A:R/A:H/A:S/A:A > FOO.TXT
        DEL C:\TEMP\*.* /F/S/Q/A:R/A:H/A:S/A:A > FOO.TXT
        ECHO. > FOO.TXT
        ECHO. > FOO.TXT
      

Putting all the commands together, your batch file would look as the sample below.

        
        ECHO OFF
        ECHO %DATE% %TIME% > FOO.TXT
        DEL C:\~*.* /F/S/Q/A:R/A:H/A:S/A:A > FOO.TXT
        DEL C:\TEMP\*.* /F/S/Q/A:R/A:H/A:S/A:A > FOO.TXT
        ECHO. > FOO.TXT
        DEFRAG /F/U/SE/SKIPHIGH C: > FOO.TXT
        SCANDISK /ALL/AUTOFIX/NOSAVE/NOSUMMARY/SURFACE > FOO.TXT
        ECHO. > FOO.TXT
        ECHO. > FOO.TXT
      

Note that is good practice to leave blank lines between sections of a batch file to make it easier to read. These lines do not affect the functionality of the batch file (no speed increase or delay). Therefore the sample above is the same as the one below, but the one below is easier on the eyes.

        
        ECHO OFF
        
        ECHO %DATE% %TIME% > FOO.TXT
        
        DEL C:\~*.* /F/S/Q/A:R/A:H/A:S/A:A > FOO.TXT
        DEL C:\TEMP\*.* /F/S/Q/A:R/A:H/A:S/A:A > FOO.TXT
        
        ECHO. > FOO.TXT
        
        DEFRAG /F/U/SE/SKIPHIGH C: > FOO.TXT
        SCANDISK /ALL/AUTOFIX/NOSAVE/NOSUMMARY/SURFACE > FOO.TXT
        
        ECHO. > FOO.TXT
        ECHO. > FOO.TXT
      

Of course, follow this instructions at your own risk. Although these commands will not normally hurt your system, do NOT blame me as I take no responsibility if something goes wrong and/or if you delete important data by mistake. Refer to the disclaimer.

As I mentioned at the beginning of this section, these instructions are for MS-DOS. Other versions of DOS are slightly different. For example, FreeDOS has a more organized directory structure and comes with C:\FDOS\TEMP where FDOS is the DOS subdirectory. I do not know if FreeDOS has a built-in facility for garbage management. If you were to adapt the previous code, make sure you understand the directory structure of the version of DOS as well as which commands and executables are available.

Versions of DOS Compatible with MS-DOS:

Versions of DOS Incompatible with MS-DOS:

MS-DOS Emulators (Command Prompt Interpreters):

          
          MOUNT X X:\GAMES
        

          
          X:
        

          
          [autoexec]
          ECHO OFF
          MOUNT X X:\GAMES
        

          
          MOUNT C X:\OpenGEM
        

          
          MOUNT A X:\[path]