What Was DOS? History, Commands and How to Run It Today
DOS, the Disk Operating System, is the text-only operating system that powered the first generation of IBM-compatible PCs. It has not been the core of Windows for more than twenty years, but its ideas are still around: drive letters, C:\ paths, file names with extensions, batch files and the command prompt all come from it. This article covers where DOS came from, what it could do, what is still true about it today, and how to run it safely on a modern PC for learning.
A short history
- 1980-81: Seattle Computer Products’ Tim Paterson wrote 86-DOS (QDOS) for the Intel 8086. Microsoft bought the rights and adapted it for IBM’s first personal computer.
- August 1981: The IBM PC launched with PC DOS 1.0. Microsoft was free to license the same system to other manufacturers as MS-DOS, and clone makers did, which helped make the “IBM-compatible” PC the industry standard.
- 1983: DOS 2.0 added hierarchical directories (folders) and support for hard disks.
- 1991-94: MS-DOS 5.0 and 6.x added memory managers, a full-screen editor, and disk utilities. MS-DOS 6.22 (1994) was the last widely used standalone version.
- 1995-2000: Windows 95, 98 and Me still started on top of a version of MS-DOS, although Windows took over most of the work.
- 2001 onwards: Windows XP and later are based on the Windows NT kernel and do not use DOS at all.
How DOS worked
DOS was a single-user, single-tasking system. It loaded a small kernel (in files such as IO.SYS and MSDOS.SYS) and a command interpreter, COMMAND.COM, which displayed the prompt (C:\>) and ran your commands. Programs ran one at a time, with direct access to the hardware, which made DOS fast and simple but also meant a misbehaving program could crash the whole machine. There was no separation like the one in user mode and kernel mode.
Memory was the constant headache. The original design addressed 1 MB, of which only 640 KB was available to programs (“conventional memory”). Later DOS versions and tools like HIMEM.SYS and EMM386.EXE squeezed more out of extended and expanded memory, and tuning CONFIG.SYS and AUTOEXEC.BAT for a game was a rite of passage.
Everyday commands
| Command | What it does | Still in Windows? |
|---|---|---|
DIR |
List files and folders | Yes (cmd.exe) |
CD / MD / RD |
Change, make, remove directories | Yes |
COPY, DEL, REN, TYPE |
Copy, delete, rename, show a file | Yes |
FORMAT, CHKDSK |
Format a disk, check a disk | Yes, with different options |
EDIT |
Full-screen text editor (from DOS 5) | A different, newer edit is included in recent Windows 11 builds |
FDISK |
Partition a hard disk | No (replaced by diskpart) |
MEM |
Show memory usage | No |
Batch files: the ancestor of scripting
DOS could run a list of commands stored in a .BAT file. The same syntax still works in Windows, which is why old batch knowledge is still useful. This small example copies a folder to a fixed backup directory; it runs in a modern Command Prompt, and is also close to something DOS 6 could execute:
@echo off
rem Copy the Documents folder to a backup drive
if not exist D:\backup mkdir D:\backup
xcopy C:\Users\Public\Documents D:\backup /s /e /y
echo Backup finished.
pauseLine by line: @echo off stops the commands from being echoed; rem starts a comment; if not exist creates the target folder if needed; xcopy copies the source folder’s contents, including sub-folders (/s /e; add /h to include hidden and system files) and overwrites without asking (/y); pause keeps the window open. Today, PowerShell is the better choice for new scripts, but batch files are still everywhere in corporate logon and installation scripts.
DOS vs the Windows command prompt
A common confusion: the Command Prompt in Windows 10 and 11 (cmd.exe) is not DOS. It is a Windows program that copies DOS-style syntax for compatibility. Windows on 32-bit x86 could run many 16-bit DOS programs through a component called NTVDM, but 64-bit Windows never included it, and Windows 11 has no 32-bit edition, so old DOS programs no longer run there directly. You need an emulator or a virtual machine.
Where DOS is still used
- Firmware and hardware utilities: some BIOS updates and diagnostics for older equipment are still distributed as bootable DOS images, often built on FreeDOS.
- Legacy and embedded equipment: some old industrial and lab machines run DOS programs because rewriting them is expensive. Such machines are a security risk and should be isolated from the network.
- FreeDOS: an actively maintained, free, MS-DOS-compatible operating system for running old software on real or virtual hardware.
- Retro computing and games: a large catalogue of classic games runs in emulators.
How to try DOS today
- DOSBox: a free, open-source x86 and DOS emulator that runs DOS programs and games on Windows, macOS and Linux without installing an operating system. Variants such as DOSBox Staging and DOSBox-X add features.
- A virtual machine: in VirtualBox, VMware or Hyper-V, install FreeDOS from its ISO image to experience a real DOS boot, with
CONFIG.SYSandAUTOEXEC.BAT. Give it a tiny disk and 32 MB of RAM; it needs very little. - Real hardware: collectors keep old PCs running. This is the most authentic and the least practical.
In DOSBox, a typical session is: mount a folder as a drive with mount c C:\dosgames, switch to it with c:, then dir and run the program. Only download software from sources you trust, since old shareware collections can contain malware.
Common questions
Is DOS still supported by Microsoft?
No. MS-DOS is discontinued, and Microsoft has released the source code of early versions (1.25 and 2.0, and later 4.0) for historical study under the MIT licence.
Should I learn DOS commands to work as a sysadmin?
Not DOS as such, but the shared batch and cmd commands are handy for Windows administration. PowerShell, covered elsewhere on this site, is where new work happens.
Keep reading
- History of Windows: Every Major Version From 1.0 to Windows 11 — How Windows grew from DOS.
- History of Operating Systems: From Batch Jobs to Unix, Windows and Cloud — The wider history of operating systems.
- Windows Boot Process Step by Step (and How to Fix Each Stage) — How a modern PC starts.
