DOSBox

DOSBox
DOSBox icon.png
DOSBox 0.74 running on Windows Vista
DOSBox 0.74 running on Windows Vista
Developer(s) Peter "Qbix" Veenstra, Sjoerd "Harekiet" van der Berg, Tommy "fanskapet" Frössman, Ulf "Finster" Wohlers
Initial release July 22, 2002; 15 years ago (2002-07-22) [1] [2]
Stable release 0.74 (May 12, 2010; 7 years ago (2010-05-12) [3])
Preview release SVN r4052 (September 20, 2017; 2 months ago (2017-09-20) [4] [5] [6])
Written in C++ [7]
Operating system Windows, macOS, Linux, Android, Chrome OS ( Gentoo Linux), AROS, AmigaOS 4, Amiga, BeOS, FreeBSD, OpenBSD, MorphOS, OS/2, RISC OS, Solaris 10
Available in English (but supports alternate keyboard layouts)
Type Virtual machine, emulator
License GNU General Public License
Website www.dosbox.com

DOSBox is an emulator program that emulates an IBM PC compatible computer running a DOS operating system. Many IBM PC compatible graphics and sound cards are also emulated. This means that original DOS programs (including PC games) are provided with an environment in which they can run correctly, even though the modern computers have dropped support for that old environment. DOSBox is free software written primarily in C++ and distributed under the GNU General Public License. DOSBox has been downloaded over 34 million times since its release on SourceForge in 2002. [8]

DOSBox can run old DOS software on modern computers which would not work otherwise, because of incompatibilities between the older software and modern hardware and operating systems.

A number of usability enhancements have been added to DOSBox beyond emulating DOS. The added features include virtual hard drives, peer-to-peer networking, screen capture and screencasting from the emulated screen.

An official version of DOSBox has not been released since DOSBox 0.74 in May 2010, although development continues in the SVN version. Forks such as DOSBox SVN Daum and DOSBox SVN-lfn provide additional features, which include support for save states and long filenames (LFN). [9]

A number of vintage DOS games have been commercially re-released to run on modern operating systems by encapsulating them inside DOSBox.

Features

DOSBox is a command-line program, configured either by a set of command-line arguments or by editing a plain text configuration file. For ease of use, several graphical front-ends have been developed by the user community. [10]

A popular feature of DOSBox is its ability to capture screenshots and record gameplay footage. The video is compressed using the lossless Zip Motion Block Video codec. [11] In its uncompressed state the footage is almost an exact replica of the actual program. The video recording feature was added in version 0.65. In earlier versions, one had to rely on custom modifications and a third-party screen recorder to record video, but the quality and emulator performance was generally very poor. [12]

The DOSBox project has a policy of not adding features that aren't used by DOS games if they take significant effort to implement, are likely to be a source of bugs or portability problems, and/or impact performance. Perhaps the most common hardware feature of DOS-era PCs that the official version of DOSBox doesn't emulate is the parallel port that was used to connect printers. As an alternative, the PrintScreen function of modern OSs can be used to capture the output of DOSBox. For similar reasons, no support for long filenames and Ctrl-Break is added into official versions, though support for them is available in some unofficial enhanced SVN builds.

Hardware emulation

DOSBox is a full CPU emulator, capable of running DOS programs that require the CPU to be in real mode or protected mode. [13] Other similar programs, such as DOSEMU or VDMs for Windows and OS/2, provide compatibility layers and rely on virtualization capabilities of the 386 family processors. Since DOSBox can emulate its CPU by interpretation, the environment it emulates is completely independent of the host CPU. [13] On systems which provide the i386 instruction set, however, DOSBox can use dynamic instruction translation to accelerate execution several times faster than interpretive CPU emulation.[ citation needed] The emulated CPU speed of DOSBox is also manually adjustable by the user to accommodate for the speed of the systems DOS programs were originally written for. [14]

DOSBox can emulate a wide range of graphics and sound hardware. Graphics emulation includes text mode, Hercules, CGA (including some composite modes and the 160x100x16 tweaked modes), Tandy, EGA, VGA (including Mode X and other tweaks), VESA, and full S3 Trio 64 emulation. [13] Sound hardware that can be emulated includes the PC speaker (played back through the host's standard sound output, not its physical internal PC speaker), AdLib, Gravis Ultrasound, Tandy, Creative Music System/GameBlaster, Sound Blaster 1.x/2.0/Pro/16, and Disney Sound Source. MIDI output through an emulated MPU-401 interface is available if the host is equipped with a physical MIDI-Out connector or a suitable software MIDI synthesizer. ( MT-32/ CM-32L emulation is included in unofficial enhanced builds, [9] but not in the official source code repository due to need for copyrighted ROM images.) Storage is handled by mapping (either through the configuration file or through a command within the emulator) a drive letter in the emulator to a directory, image file, floppy disk drive, or CDROM drive on the host. A permanently mapped Z: drive stores DOSBox commands and startup scripts.

Emulation of Voodoo cards is in development[ when?]. This should give not only support for games that use the Glide API, but also provide Direct3D support to Win9x guests.

DOSBox, unlike many other emulators, can simulate peer-to-peer or Internet/ Intranet networking. This includes modem simulation over TCP/IP, allowing for DOS modem games to be played over modern LANs or the Internet, and IPX network tunneling, which allows for old IPX DOS multiplayer games to be played as UDP/IP over modern LANs or the Internet. Win32 and Linux specific builds support direct serial port access. Some third-party patches also allow DOSBox to emulate an NE2000-class network interface card as a passthrough to the host computer's own network card, essentially allowing full internet connectivity (for example, using Windows 3.1 and Trumpet Winsock) and web browsing using programs such as Netscape Navigator, although this is more of a curiosity than a useful feature.

DOSBox is capable of timing-compatible implementation of the serial ports, which can enable older hardware and software dependent on serial port timing to work; however, some USB devices that are supported by the host OS can act as a replacement for older serial port devices when using the emulator.

OS emulation

DOSBox provides a high level emulation of the DOS and BIOS interrupts, and contains its own internal DOS-like shell. This means that it can be used without owning a license to any real DOS operating system. Most commands that are typically used in installer batch files are supported, but many of the more advanced commands of later DOS versions (e.g. post- Windows 98 DOS shells) are not. In addition to its internal shell, it also supports running image files of games and software originally intended to start without any operating system. The DOS emulation enables DOSBox to mount folders of the host OS as virtual drives.

It can also boot disk images with real DOS environments (e.g. MS-DOS, PC DOS, DR-DOS or FreeDOS) as well as other operating systems, including CP/M-86, Windows 3.1x, and Windows 95. Since DOSBox is not optimized for this mode of operation, booting any real OS inside DOSBox entails the loss of the use of directory-based virtual hard drives and some other enhancements that aren't directly compatible with the way real operating systems access hardware. For the kinds of hardware (such as disk drive controllers and computer mice) that are almost always accessed by DOS-based games through DOS and/or through the BIOS and/or through a software driver, rather than through direct access to hardware registers, DOSBox generally provides no hardware-level emulation. This means that the direct use of copy-protected physical media or of floppy disks in non-standard formats is generally not possible from DOSBox.

Configuration

The DOSBox installer under Windows creates shorthand links to launch DOSBox options, console mode, noconsole mode, recordings, and keyboard mappings. DOSBox can automatically handle most host keyboard and mouse events, and also offers to define special mappings, e.g., Ctrl-Alt-Del or the Ctrl-F10 "host key" to release a mouse captured in the guest VDM cannot be used directly in the guest. Another example is to emulate a QWERTY-layout in the guest with a QWERTZ-keyboard in the host, or vice versa, if the DOSBox default for the host does not work in an old application.

Under Windows the DOSBox console window shows stdout and stderr text messages for a running guest VDM. The DOSBox noconsole shorthand link uses command line option -noconsole to disable this console window, redirecting any console messages to host files stdout and stderr. [15]

The options shorthand link allows to edit the (per user) DOSBox configuration, an ordinary text file with sections for the emulated machine, video, sound, and so on. The [autoexec] section is executed as AUTOEXEC.BAT after showing the DOSBox intro message. The [autoexec] section could CLS the intro message, query or set the emulated VER (default: 5.00 as in Windows NT 5.x VDMs), MOUNT folders or devices as DOS drives (e.g., mount a a:\ -t floppy), IMGMOUNT an ISO image, switch the current drive from DOSBox Z: to a mounted C:, set the PATH, etc. Special DOSBox commands allow manipulating configuration options within a guest VDM, there is no corresponding virtual CONFIG.SYS file.

The optional first argument of DOSBox in a shorthand link or on the command line can give a host directory or file. This has the same effect as explicitly mounting the host folder as drive C: in the guest VDM, switch to this drive, and start the DOS-executable file. Command line option -exit can automatically terminate DOSBox after this executable file. Command line options -c something or -c "make it so" can specify commands run before this executable file, e.g., set environment variables.

This approach covers many common scenarios without editing configuration files, and it allows to share one DOSBox configuration file with several DOS applications. For applications supporting their own command line arguments such as DEBUG a DOSBox command line option -c "c:\debug arguments" can be used.

Command line option -securemode disables the [autoexec] section in the configuration, and does not offer to MOUNT host folders within the guest VDM. [15]

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