Screenshot showing the boot screen, command-line interface, and directory structure of MS-DOS 6
Screenshot showing the boot screen, command-line interface, version information, and directory structure of FreeDOS
Screenshot showing Digital Research Apple CP/M on a Z-80 SoftCard for the Apple II
The IBM Personal Computer (IBM 5150 PC)
A sample SCP 86-DOS session (simulated)
Digital Research CP/M-86 for the IBM Personal Computer Version 1.0
OS/2 1.0 featured a text mode interface similar to MS-DOS.
Arachne web browser

Platform-independent acronym for disk operating system which later became a common shorthand for disk-based operating systems on IBM PC compatibles.


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Mass-market operating system created in 1974 for Intel 8080/85-based microcomputers by Gary Kildall of Digital Research, Inc. Initially confined to single-tasking on 8-bit processors and no more than 64 kilobytes of memory, later versions of CP/M added multi-user variations and were migrated to 16-bit processors.

A screenshot of CP/M-86
CP/M advertisement in the 29 November 1982 issue of InfoWorld magazine
Apple CP/M Card with manual
CP/M Plus (CP/M 3) System Guide
DEC PRO-CP/M-80 floppy-disk distribution for the Z80-A co-processor in a DEC Professional 3xx series
Sanco 8001 computer, running under CP/M 2.2 (1982)
CP/M cartridge for the Commodore 64
Screenshot showing a CP/M 3.0 directory listing using the command on a Commodore 128 home computer
CP/M advertisement in the 11 December 1978, issue of InfoWorld magazine
Distribution 5 1/4 inch diskettes and packaging for the last version (version 4) of WordStar word processing program released for 8-bit CP/M
MBASIC text output displayed on a monochrome monitor typical for that time.
CP/M derivate SCP running on an East German robotron PC 1715
CP/J version 2.21 running on an Elwro 804 Junior

CP/M was eventually displaced by DOS following the 1981 introduction of the IBM PC.


PhysTechSoft PTS - DOS Version 7.00 Revision 0 (PTS-DOS 7.0 Beta version)
Paragon Technology Systems PTS/DOS 6.51CD & S/DOS 1.0

PTS-DOS (aka PTS/DOS) is a disk operating system, a DOS clone, developed in Russia by PhysTechSoft and Paragon Technology Systems.


Privately held software company specializing in power failsafe and high performance software for preserving data integrity in embedded systems.

Datalight's initial products were two DOS applications: the Datalight Small-C compiler and the Datalight C-Bug debugger.


Acronym for IBM Personal Computer Disk Operating System, is a discontinued disk operating system for IBM PC compatibles.

IBM PC DOS command line
User manual and diskette for IBM PC DOS 1.1

The collective shorthand for PC DOS and MS-DOS was DOS, which is also the generic term for disk operating system, and is shared with dozens of disk operating systems called DOS.

Intel 8080

Second 8-bit microprocessor designed and manufactured by Intel.

An Intel C8080A processor variant with white ceramic package, solder seal metal lid, and gold pins.
i8080 microarchitecture
8080 Pinout
AMD Am9080
CEMI MCY7880 (Poland)
Kvazar Kiev K580IK80 (Soviet Union)
Mitsubishi Electric M5L8080
National Semiconductor INS8080
Siemens SAB8080
Signetics MP8080
Tesla (Czechoslovak company) MHB8080
Texas Instruments TMS8080

The 8080 is used in many early microcomputers, such as the MITS Altair 8800 Computer, Processor Technology SOL-20 Terminal Computer and IMSAI 8080 Microcomputer, forming the basis for machines running the CP/M operating system (the later, almost fully compatible and more able, Zilog Z80 processor would capitalize on this, with Z80 & CP/M becoming the dominant CPU and OS combination of the period circa 1976 to 1983 much as did the x86 & DOS for the PC a decade later).

Filename extension

Suffix to the name of a computer file .

Screenshot of a Windows command shell showing filenames in a directory

Under Microsoft's DOS and Windows, extensions such as, or indicate that a file is a program executable.

Intel 8086

16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released.

A rare Intel C8086 processor in purple ceramic DIP package with side-brazed pins
Intel 8086 CPU die image
The 8086 pin assignments in min and max mode
Simplified block diagram over Intel 8088 (a variant of 8086); 1=main & index registers; 2=segment registers and IP; 3=address adder; 4=internal address bus; 5=instruction queue; 6=control unit (very simplified!); 7=bus interface; 8=internal databus; 9=ALU; 10/11/12=external address/data/control bus.

The authors of most DOS implementations took advantage of this by providing an Application Programming Interface very similar to CP/M as well as including the simple .com executable file format, identical to CP/M.


DOSBox 0.74-3 opening screen
DOSBox 0.74-3 opening screen

DOSBox is a free and open-source emulator which runs software for MS-DOS compatible disk operating systems—primarily video games.


Firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the booting process (power-on startup).

A pair of AMD BIOS chips for a Dell 310 computer from the 1980s
Boot process
BIOS chips in a Dell 310 that were updated by replacing the chips
Award BIOS setup utility on a standard PC
BIOS replacement kit for a Dell 310 from the late 1980s. Included are two chips, a plastic holder for the chips, and a chip puller.
American Megatrends BIOS 686. This BIOS chip is housed in a PLCC package in a socket.
Compaq Portable 386 BIOS
An American Megatrends BIOS showing an "Intel CPU uCode Loading Error" after a failed attempt to upload microcode patches into the CPU
A detached BIOS chip

In the era of DOS, the BIOS provided BIOS interrupt calls for the keyboard, display, storage, and other input/output (I/O) devices that standardized an interface to application programs and the operating system.

Disk partitioning

Creation of one or more regions on secondary storage, so that each region can be managed separately.

GParted is a popular utility used for disk partitioning
A GRUB startup menu showing Ubuntu Linux (with three different boot modes) and Windows Vista options

With DOS, Microsoft Windows, and OS/2, a common practice is to use one primary partition for the active file system that will contain the operating system, the page/swap file, all utilities, applications, and user data.