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FastBasic - Fast BASIC interpreter for the Atari 8-bit computers

This is a fast interpreter for the BASIC language on the Atari 8-bit computers and the Atari 5200 console.

The current features are:

  • Support for Atari floating point and 16bit integer variables;
  • Support for string arrays, substrings and concatenation;
  • Small size (currently the full floating point IDE is 9.3k, the integer IDE is 8k, and the runtime is less than 3k);
  • Fast execution (currently, 2 times faster than compiled TurboBasicXL in the "sieve.bas" benchmark, 6 times faster than OSS Integer Basic);
  • Modern syntax (no line numbers, many control structures);
  • Procedures with parameters and short calling syntax;
  • Feels "alike" TurboBasicXL, with many of the extended statements;
  • Integrated editor and compiler running in the Atari 8-bit;
  • A cross-compiler is available that directly compiles sources to Atari executables on any modern PC;
  • Statements for Player/Missile graphics and Display List Interrupts.

For support, use the GitHub bug-tracker or see the AtariAge thread at:


There is a full manual with all the supported syntax in the file

To use the cross-compiler, download from the releases and see compiler/ for instructions.

For the Atari 5200 support, read the Atari 5200 manual appendix.

Sample files

There are samples for the integer only compiler and for the floating point compiler, in addition to more test programs in the tests folder.


FastBasic is free software under the terms of the GNU General Public License, either version 2 or later, see the file LICENSE for the full text.

The runtime is also under the following linking exception:

In addition to the permissions in the GNU General Public License, the authors give you unlimited permission to link the compiled version of this file into combinations with other programs, and to distribute those combinations without any restriction coming from the use of this file. (The General Public License restrictions do apply in other respects; for example, they cover modification of the file, and distribution when not linked into a combine executable.)

This means that you can distribute the compiled result of any program written by you under any license of your choosing, either proprietary or copyleft.

Compiling the sources

To compile the sources, you need:

  • Host build tools (make & gcc) to build the syntax generator
  • mkatr, from to build the Atari disk image (ATR) file.

Then, type make to build all sources to a "fastbasic.xex" file and a "fastbasic.atr" disk image.

There is also a test-suite that tests various source files compiled with the Atari compiler and the cross compilers, you can run the test-suite by typing make test