1. Introduction
2. What You Will Need
3. Installation
4. Games
5. Starting A Game
6. Changing Options
7. Settings File
8. Keyboard Layout
9. Event Remapping
10. Integrated Debugger
11. Game Properties
12. Stelladaptor Support
13. Acknowledgments
14. License and Disclaimer

A Brief History of the Atari 2600

In the early 1970's, video arcade games gained commercial success for the first time. The American public was introduced to Pong, Tank, and other interactive video games which populated amusement parks, bars, and arcades. The games were successful enough to create interest for home versions, so in 1975 Atari released Home Pong and it was a smash hit. Other companies such as Magnavox and Coleco followed suit and released their own dedicated console games. Then in 1976, Fairchild Camera and Instrument introduced the Channel F system, the first cartridge based home video game system. The industry recognized that cartridge systems were the future of video gaming, and began development in that direction. In January 1977, RCA released the Studio II, another cartridge based system, although it only projected in black and white and seemed to be focused on educational titles. Then, in October 1977, Atari released the Atari VCS (Video Computer System) with an initial offering of nine games. This system, later renamed the Atari 2600, took the industry by storm and dominated the marketplace for years to come.

Because of oversupply, the Christmas season of 1977 was very rough on the video game industry, and the Atari 2600 was the only system that managed to emerge unscathed. Atari enjoyed strong sales in 1978 and a fantastic holiday season, as Atari released more games such as Outlaw, Spacewar, and Breakout. Internally however, Atari was at odds. Nolan Bushnell, the inventor of pong and founder of Atari, wound up leaving the company and purchased Pizza Time Theater, which later became the successful Chuck E. Cheese! In 1979 Atari continued their trend and released 12 more games which met with continued success. However, Atari was now facing some stiffer competition from the Mattel Intellivision and the Magnavox Odyssey2.

Atari needed a mega-hit in 1980 in order to squash the competition, and they found it in the home version of a game from Japan called Space Invaders. It was so popular that people were buying the Atari 2600 just so they could play Space Invaders at home. Following that, Atari released Adventure, which was the first video game to contain an Easter Egg - placing an object in a certain area revealed the programmer's name, Warren Robinett. 1980 was important for another reason - the creation of the first ever third party software producer, Activision. The company was formed by four Atari employees who were unsatisfied with the working conditions at the company. They released four games initially: Dragster, Fishing Derby, Checkers and Boxing. The games were very well received by the public, and revealed that the Atari 2600 was capable of better games than Atari themselves had been producing. Atari tried to prevent Activision from selling games, but they failed and Activision grossed $70 million that year.

By 1981, the video game industry was basically a horse race between the 2600 and the Intellivision. While the Intellivision was technologically superior in some respects, the 2600 continued to lead in sales. Atari released the home version of Asteroids, which was a huge success. Inspired by the success of Activision, another software development group called Imagic was formed. They would not release any games until 1982 however. Another company, Games by Apollo, was formed in Texas and released several games that year.

Coleco entered the market in 1982 with the release of the graphically superior Colecovision. To combat this new system, Atari produced the 5200, a technologically comparable system. The 2600 dropped $100 in price in order to remain competitive. Then a company called Arcadia released a peripheral called the Supercharger which played games in an audio cassette medium. This allowed for multiple loads and expanded the 2600's capabilities.

Atari released Pac-Man and E.T. that year, two incredibly hyped games which were critical flops. Although Pac-Man sold many copies, it was considered to be a poor translation of the arcade hit. However, there were many fantastic games produced for the 2600 during this period, and it was still selling strong.

Ever since the inception of Activision, Atari had been fighting to keep third parties from producing cartridges which they felt were stealing profits from them. Finally the issue was settled when Atari agreed to allow third party manufacturing in exchange for a royalty. Suddenly software companies began popping up all over, and 1982 saw releases from companies like Venturevision, Spectravision, Telesys, CBS, 20th Century Fox, US Games, M Network, Tigervision, Data Age, Imagic and Coleco. There was even a company that released a line of X-Rated games for the 2600 called Mystique. The year was financially successful for Atari, however there seemed to be a glut of software. Although there were many quality titles still produced, there was an increasing number of rushed games as manufacturers attempted to cash in on the craze.

More companies jumped on the band wagon in 1983. Zimag, Ultravision, Amiga, and others were also producing games and peripherals. It seemed as if there was just too much product to meet the demand, and as it turned out there was. By the end of the year, companies began folding. US Games, Data Age, Games by Apollo, Telesys and others all closed their doors from poor sales. A video game crash was occurring, and all companies were taking it on the chin.

1984 was a much more subdued year for the Atari 2600, and the price of the system had now dropped to $40-$50. Many were saying that the video game industry was dead. However, Atari surprised everyone by announcing the release of the 7800, and also promising more 2600 games with improved graphics and sound. Unfortunately, neither of these things happened in 1984 because Atari sold their home video game division to Jack Tramiel who believed that home computers would replace video game systems. No further mention of the 2600 or 7800 was made that year, and it appeared that they might be dead.

1985 was another very quiet year for Atari and video games in general, and only a few games were released for the 2600. Activision produced Cosmic Commuter and Ghostbusters, but with little fanfare or marketing, these games did not sell well. However, because of the huge game library and cheap price, Atari still sold over a million 2600 consoles in 1985.

There were very few plans for home video game systems by any company in 1986, since the market appeared to be dead. Then, to most people's surprise, Nintendo brought the NES to America and it was a smash hit, proving that video games still had a place in the US. Atari decided that maybe it would be a good idea to release the 7800 units it had in storage, and produce some more 2600 games. The 7800 was released with only 3 games initially available, although it was compatible with the 2600 library. They also redesigned the 2600 as the 2600 Jr., a machine with the same abilities, but a new look and marketing campaign. It was sold for less than $50.

Video games were once again selling phenomenally in 1987. Atari released several new titles, including Jr. Pac-Man, and also licensed a number of games from other companies such as Donkey Kong and Q*Bert. These new titles sold for $10-$15. Interestingly, a number of titles began appearing again from third part companies such as Epyx, Froggo, and Exus. It seemed that the 2600 was not dead yet!

In 1988, Atari rehired Nolan Bushnell and announced a number of new titles, including Secret Quest, a game written by Mr. Bushnell himself. Atari continued to manufacture these games even until 1989. However, it was apparent that the 2600, after its introduction over a decade ago, was finally at the end of its run. Although it was still produced and marketed outside of the US, the Atari 2600 finished its run in America. No other console has had such a long history or sold as many systems in the U.S.

Today, the 2600 still has a large number of fans who remember the countless games played over the years, and the years to come. There are even games being produced by hobbyists, some of them quite professionally, being released on newly burnt cartridges with labels and manuals. And the recent trend in retrogaming has brought many more video game fans to rediscover the 2600, and it continues to live on 22 years after its release!

Alexander Bilstein
February 1999

1. Introduction

Stella is a freely distributed multi-platform Atari 2600 VCS emulator; originally developed for Linux by Bradford W. Mott. Stella allows you to enjoy all of your favorite 2600 games once again by emulating the 2600's hardware with software. Stella is written in C++, which allows it to be ported to other operating systems and architectures. Since its original release Stella has been ported to AcornOS, AmigaOS, DOS, FreeBSD, Linux, MacOS, OpenStep, OS/2, Sega Dreamcast, Unix, and Windows.

New in Release 2.0

• Added integrated GUI. Stella is now a fully graphical application, and all settings can be changed dynamically while the application is running. That means the commandline is no longer required (but support is still there for those that want to use it).
• Added ROM launcher. You can now exit a game and start playing another one from directly within Stella (you no longer have to quit Stella and restart it).
• Because of the integrated GUI and ROM launcher, StellaX and KStella (the Windows and Linux frontends) have been discontinued. The OSX port now uses the launcher as well.
• FIXME - add info about integrated debugger
• Further consolidation and integration of SDL. This should lead to faster operation and a more consistent look for all ports.
• Added ZIP support. Stella can now open ROM's compressed in zip format.
• Added Alt/Shift-Cmd z, x, c, v, b, n keys to enable/disable the P0, P1, M0, M1, BL, PL bits in the TIA, respectively.
• Added Alt/Shift-Cmd . key to disable all bits in the TIA.
• Added Alt/Shift-Cmd / key to enable all bits in the TIA.
• Added Alt/Shift-Cmd g key to switch dynamically switch between software and OpenGL modes while Stella is running.
• Added Ctrl/Cmd r key to reload the ROM currently being emulated.
• Added Alt/Shift-Cmd s key to merge the current game properties into the properties file.
• Added help commandline argument. Launching Stella from the commandline with no options now starts Stella in ROM launcher mode, instead of showing help (as in previous versions).
• Added the following commandline arguments for developers: pro, type, ld, rd, tv, lc, rc, bc, format, xstart, ystart, width height, cpu, hmove. Developers can consult the manual for further details.
• Removed mergeprops commandline argument, since there are now dedicated keys to do either save or merge game properties.
• Removed grabmouse and hidecursor commandline arguments. Stella will now automatically decide when to use these settings. You can still use Ctrl/Cmd g to grab/ungrab the mouse.
• Fixed framerate when switching between NTSC and PAL modes. Stella now uses the correct framerate based on the format of the ROM.
• Fixed some 64-bit issues. Stella now compiles and runs correctly on AMD64 and PPC64 systems.
• Updated the Stella manual with pictures of the new integrated GUI.

Features

• High speed emulation using optimized C++ code
• Supports high quality sound emulation using Ron Fries' TIA Sound Emulation library
• Emulates the Atari 2600 Joystick Controllers using your computer's keyboard or joysticks
• Emulates the Atari 2600 Keyboard Controllers using your computer's keyboard
• Emulates one Atari 2600 Paddle Controller using your computer's mouse
• Support for real Atari 2600 controllers using the Stelladaptor
• Emulates the Atari 2600 Driving Controllers using your computer's keyboard or joysticks
• Emulates the CBS Booster-Grip Controller using your computer's keyboard or joysticks
• Supports cartridges using Atari's standard 2K and 4K format
• Supports cartridges using Atari's 8K, 16K, and 32K bank-switching schemes
• Supports cartridges using Activision's 8K bank-switching scheme (Robot Tank and Decathlon)
• Supports cartridges using CBS Electronics' 12K bank-switching scheme
• Supports cartridges using Chris Wilkson's Megacart 128K bank-switching scheme
• Supports cartridges using Commavid bank-switching scheme
• Supports cartridges using M-Network's 16K bank-switching scheme
• Supports cartridges using Parker Brothers' 8K bank-switching scheme
• Supports cartridges using Tigervision's bank-switching scheme with up to 512K ROM
• Supports cartridges using UA Limited bank-switching scheme
• Supports Supercharger single-load and multi-load games
• Supports property file for setting the properties associated with games
• Supports user specified frame rate
• Supports the NTSC and PAL television palettes
• Supports several "undocumented features" of the TIA graphics chip used by some games
• TIA emulation supports full collision checking

2. What You Will Need

The following sections outline the basic system requirements for running Stella under various operating systems.

Note that for this version of Stella, you are required to have a stella.pro file. It is no longer optional as it was for past versions.

General (required for all versions of Stella)

• Enough RAM for the OS + 16MB RAM for the emulation; 32MB highly recommended
• 15 bit color minimum; 16 bit color graphics card highly recommended
• SDL version 1.2.0 or greater
• Latest versions of the libpng and zlib libraries
• Joysticks or gamepads are highly recommended
• Mouse or Stelladaptor with real paddles required for paddle emulation
• Some ROM images (no, we won't tell you where to find them)

Linux/UNIX

The Linux version of Stella is designed to work on a Linux Workstation with the following:

• Linux Kernel 2.4.x, Linux Kernel 2.6.x is highly recommended
• GNU C++ compiler version 2.95 and the make utility are required for compiling the Stella source code; GNU C++ compiler version 3.2.x or later is highly recommended
• Pentium class machine required (Stella may compile on other architectures, but it hasn't been extensively tested)

Macintosh

The Mac version of Stella is designed to work on a Power Macintosh with the following:

• Mac OSX 10.1 or Above
• 500 MHz G4 PPC processor or above (Stella may work with a G3 processor, but this is still a work-in-progress)

Windows

The Windows version of Stella is designed to work on Windows 95/98/ME/2000/XP with the following:

• Visual C++ 7 or MinGW compiler is required to compile the Stella source code
• Pentium class machine required; OpenGL accelerated video card highly recommended
• SDL version 1.2.8 or greater (or included SDL.dll) required for Stelladaptor support

3. Installation

Stella is distributed in both source and binary form. Once you have a Stella distribution you should follow the instructions for your operating system given below.

If you have a supported joystick and driver installed and SDL can access the device, you can play games using joysticks.

Currently, sound is supported using SDL. As long as SDL can detect your sound card, Stella will be able to produce sound.

Linux/UNIX

• Compressed tarball (stella-release-src.tar.gz)
1. Extract files from the distribution:

      tar zxvf stella-release-src.tar.gz

2. Change directories to the stella-release/src/build directory
3. Edit the makefile to meet your needs
4. Build the executable with the following command:

      make linux (or make linux-gl)

5. Copy the executable to a directory that's in your path:

      cp stella /usr/local/bin

6. Copy the supplied stella.pro properties file to the system-wide location:

      cp stella.pro /etc

   or to your home directory:

      mkdir ~/.stella
      cp stella.pro ~/.stella

• Source RPM (stella-release-1.src.rpm)
1. Rebuild the archive with the following command:

      rpmbuild --rebuild stella-release-1.src.rpm

2. Follow the instructions under Binary RPM to install the stella-release-1.ix86.rpm file
• Binary RPM (stella-release-1.ix86.rpm)
1. Install the binary RPM with the following command:

      rpm -Uvh stella-release-1.ix86.rpm

Macintosh

To install the Mac binary, simply download the DMG disk image. Mount the disk image, then copy the StellaOSXxxx folder to your hard drive.

Windows

• Compressed tarball (stella-release-src.tar.gz)
1. Extract files from the distribution using Winzip, Total Commander, or some other archiving program that supports gzipped tar files
2. If compiling the Stella executable using MinGW:
• Change directories to the stella-release/src/build directory
• Edit the makefile to meet your needs
• Build the executable with the following command:

     make win32 (or make win32-gl)

• Copy the Stella (commandline executable) and stella.pro files to some directory
3. If compiling using Visual C++ 7:
• Open the stella-release/src/win32/Stella_Emulator.sln file using Visual C++ 7
• Build the 'Stella' solution
• Copy the Stella.exe and stella.pro files to some directory
• Binary ZIP file (stella-release-win32.zip)
1. Unzip the binary ZIP file using Winzip or Total Commander and copy that directory somewhere

4. Games

Stella allows you to play games using ROM images of cartridges and cassettes.

Cartridges

Most games for the Atari 2600 came on cartridges. A cartridge usually consists of a single Read Only Memory (ROM) chip which contains the data and code for the game. Plugging a cartridge into the Atari 2600 allows the 2600's microprocessor to access the program stored on the cartridge.

In a similar way you must "plug" a copy of a cartridge into Stella when you want to play it. Having a ROM image, BIN file, of the cartridge allows you to do this. A ROM image is a file, which contains the actual data and code read from the cartridge. There are several ways to obtain a ROM image of a cartridge:

1. If you're handy with a soldering iron then you can design and build a device that plugs into the printer port of a PC and read the data from the cartridge
2. You can purchase the Atari 2600 Action Packs by Activision and use their ROM images
3. You can search around the internet and find ROM images to download

WARNING: It is illegal to use ROM images of games that you do not actually own since these games are still copyrighted.

Supercharger Cassettes

Supercharger games were not stored on cartridges instead they were stored on cassette tapes. The Supercharger, which plugged into the Atari 2600's cartridge slot, loaded games into its 6K of Random Access Memory (RAM) using a standard audio cassette player. The Supercharger also supported multi-loading, which allowed games to be broken into several segments and loaded at different times. This was useful for large games which had distinct parts such as role playing games.

Most of the available Supercharger ROM images are stored in 8448 bytes files. However, ROM images of multi-load games are sometimes stored in a set of 8448 byte files. The names of these files have a two character sequence number in them which indicates what load they are. The sequence starts with zero, skips a few numbers and then increments by one.

Stella supports multi-load games, however, the set of ROM images must be combined into a single ROM image file. For example to create a multi-load ROM image file for Survival Island you would do the following under Unix:

   % cat survivl0.bin survivl6.bin survivl7.bin > survivl.bin

   % copy /b survivl0.bin+survivl6.bin+survivl7.bin survivl.bin

Once you have the multi-load ROM image file, survivl.bin in this case, you can play the game using it.

5. Starting A Game

Once Stella is installed and you have some ROM images you're ready to start playing.

Integrated GUI

As of Stella version 2.0, there is an integrated GUI for all ports. This means that using the commandline is no longer required (but commandline support is still included for those who want to use it).

If you start Stella and do not specify a ROM image, it will start in 'ROM Launcher' mode:

The ROM and snapshot settings may be changed by clicking the 'Options' button:

Selecting a new path for ROM or snapshots is done by clicking the 'Path' button(s):

Once a ROM directory has been selected, clicking 'Reload' will update the ROM listing. You can start emulation by selecting a ROM and pressing 'Enter', clicking 'Play' or double-clicking a ROM.

Command Line

Stella can also be used from the commandline (assuming your operating system has a commandline). When using this mode, the ROM launcher is disabled.

To run Stella from the commandline, use the following format:

   stella [options ...] filename.bin

Options ('0' or 'false' indicates false, '1' or 'true' indicates true, others are self-explanatory):

-video <soft|gl>

-video_driver <windib|directx>

-gl_filter <nearest|linear>

-gl_aspect <number>

-gl_fsmax <0|1>

-zoom <size>

-fullscreen <0|1>

-grabmouse <0|1>

-palette <original|standard|z26>

-framerate <number>

-sound <0|1>

-fragsize <number>

-volume <number>

-paddle <0|1|2|3>

-showinfo <0|1>

-mergeprops <0|1>

-accurate <0|1>

-ssdir <path>

-ssname <romname|md5sum>

-sssingle <0|1>

-listrominfo

-help

If developer support was included in Stella, the following developer commandline arguments are also available. Note that in all cases, the values supplied to the arguments are not case sensitive.

-pro <props file>

-type <type>

-ld <A|B>

-rd <A|B>

-tv <Color|BlankAndWhite>

-lc <type>

-rc <type>

-bc <type>

-format <NTSC|PAL>

-xstart <number>

-ystart <number>

-width <number>

-height <number>

-cpu <High|Low>

-hmove <Yes|No>

6. Changing Options

As of version 2.0, all settings can be changed within the integrated Options GUI while Stella is running. The options are documented elsewhere in this manual and are generally self-explanatory.

Video Options dialog:

Audio Options dialog:

Game Information dialog:

Help dialog:

About dialog:

7. Settings File

Stella will remember when you change a setting either at the command line or while the emulation is running, and use the settings the next time you start the emulator. The settings are saved in a text file which can be edited outside of Stella. This file can contain your default options, and eliminates the need to specify them on the command line. Any options specified on the command line will override those in the settings file.

The syntax for the settings file is very straightforward. Any line starting with a ';' character is considered a comment and is ignored. Other lines must be of the form: command = value, where command is the same as that specified on the command line (without the '-' character), and value is dependent on the command.

For example, the following table illustrates how command line and settings entries are similar:

The settings file has a special name/location depending on which version of Stella you use:

Linux/UNIX

The Linux and UNIX version of Stella searches for the stellarc file in two places. First, it will look for stellarc in your $HOME/.stella directory. Then, it will look for stellarc in the /etc directory.

Macintosh

The Macintosh version does not use an INI file, but stores it preferences in the expected location for application preferences, in the Users home directory, in the Library/Preferences/StellaOSX.plist file.

Windows

The Windows version of Stella looks for the stella.ini file in the same directory containing the application. Future versions of Stella for Windows may look in user-specific locations (C:\Documents and Settings\...).

8. Keyboard Layout

The Atari 2600 console controls and controllers are mapped to the computer's keyboard as shown in the following tables.

As of Stella 1.4, most of these events can be remapped to other keys on your keyboard or buttons on your joystick (see Section 9 - Event Remapping). The tables below show the default settings.

Console Controls

Joystick Controller

Booster-Grip Controller

Driving Controller

Keypad Controller

Developer Keys (can't be remapped)

The following keys are activated only if developer support has been included:

Other Keys (can't be remapped)

9. Event Remapping

This version of Stella has event remapping. Almost every event in the emulator can be remapped to another key on the keyboard or to buttons on up to four joysticks/gamepads (see Section 8 - Keyboard Layout for those event which can/cannot be remapped).

To remap an event:

1. Start playing a game (ie, start the emulation).
2. Enter options mode be pressing Tab.
3. Click the 'Event Mapping' button.
4. Select event you want to remap and click the 'Map' button.
5. Press a key or a joystick button, and that key/button will be bound to the selected event.
6. Erase a mapping by clicking 'Erase', or cancel a remap in progress by clicking 'Cancel'.
7. Reset default mappings by clicking 'Defaults'.
8. Change mouse/paddle emulation in the 'Mouse is paddle' dropdown box.

The following screenshots illustrate the event remapping process:

10. Integrated Debugger

11. Game Properties

Stella uses game properties to specify the "best" emulator settings for a game. As of Version 1.2 of Stella, there are no longer any properties built-in. You must use the included stella.pro file. Otherwise, the emulator will try to guess the best settings for the game.

Linux/Unix

The Linux and Unix versions of Stella looks for the property file in your $HOME/.stella directory. If this file is not found there, Stella will look in the /etc/ directory.

Macintosh

The Mac version of Stella looks for the property file in the directory containing the application.

Windows

The Windows version of Stella looks for the property file in the same directory containing the application. Future versions of Stella for Windows may look in user-specific locations (C:\Documents and Settings\...).

Property File

A property file consists of some number of blocks. Each block in the file contains the properties for a single game. For example the general format of a property file is:

   ; Comments
   "Cartridge.Name"      "Value"
   "Property"            "Value"
   ""

   ; Comments
   "Cartridge.Name"      "Value"
   "Property"            "Value"
   ""

   . . .

   ; Comments
   "Cartridge.Name"      "Value"
   "Property"            "Value"
   ""

Every block in the property file must have a unique value for the Cartridge.Name and Cartridge.MD5 properties.

Properties

Each block in a property file consists of a set of properties for a single game. Stella supports the properties described below:

12. Stelladaptor Support

Stella supports real Atari 2600 joysticks, paddles and driving controllers using the Stelladaptor device.

Stella can use up to two Stelladaptors; any extra ones are ignored. Stelladaptor devices will be automatically detected and configured. Devices can be plugged/unplugged while the emulation is running; Stella will detect the change and act accordingly.

The detection and configuration is as follows:

• The first Stelladaptor found will act as the left game port on a real Atari. Depending on the device, Stella will detect it as either the left joystick, paddles 1 & 2, or the left driving controller.
• The second Stelladaptor found will act as the right game port on a real Atari. Depending on the device, Stella will detect it as either the right joystick, paddles 3 & 4, or the right driving controller.
• Any other Stelladaptors will be ignored.

13. Acknowledgments

Bradford W. Mott started developing Stella during the fall of 1995 and since then a number of people from around the world have contributed to the project. Some people have provided technical help while others have offered suggestions and praise. The Stella Team is grateful for all the help and support it has received over the years. The following is an incomplete list of the people who have played a part in bringing Stella to you:

14. License and Disclaimer

GNU GENERAL PUBLIC LICENSE

Version 2, June 1991

Copyright (C) 1989, 1991 Free Software Foundation, Inc.  
59 Temple Place - Suite 330, Boston, MA  02111-1307, USA

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.

Preamble

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.

When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.

We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.

Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.

Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.

The precise terms and conditions for copying, distribution and modification follow.

TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

0. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The "Program", below, refers to any such program or work, and a "work based on the Program" means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term "modification".) Each licensee is addressed as "you".

Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.

1. You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program.

You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.

2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions:

• a) You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.

• b) You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.

• c) If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.)

Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.

In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.

3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following:

• a) Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

• b) Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

• c) Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.)

If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.

4. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

5. You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it.

6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License.

7. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program.

If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.

It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.

This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.

8. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License.

9. The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and "any later version", you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.

10. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally.

NO WARRANTY

11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.