Symbolics developed Genera based on this foundation of the MIT Lisp machine operating system। It sold the operating system and layered software। Some of the layered software has been integrated into Genera in later releases. Symbolics improved the operating system software from the original MIT Lisp Machine and expanded it. The Genera operating system was only available for Symbolics Lisp Machines and the Open Genera virtual machine.
Symbolics Genera has a large number of features and supported all the versions of various hardware that Symbolics built over its lifetime. Its source code is more than a million lines of code (the number depends on the release and what amount of software is installed). Symbolics Genera was published on tape and CD-ROM. The release of the operating system also provided most of the the source code of the operating system and its applications. The user has free access to all parts of the running operating system and can write changes and extensions. The source code of the operating system is divided into systems. These systems bundle sources, binaries and other files. The system construction toolkit (SCT) maintains the dependencies, the components and the versions of all the systems. A system has two numbers: a major and a minor version number. The major version number counts the number of full constructions of a system. The minor version counts the number of patches to that system. A patch is a file that can be loaded to fix problems or provide extensions to a particular version of a system.
Symbolics developed a version of Genera, called Open Genera that included a virtual machine that enables the execution of Genera on DEC Alpha based workstations. Symbolics also developed a new operating system called Minima in Common Lisp (used for embedded applications). Symbolics also developed several extensions and applications for Genera that were sold separately (like the Symbolics S-Graphics suite).
The original Lisp Machine operating system was developed in Lisp Machine Lisp and using the Flavors object-oriented extension to Lisp Machine Lisp. Symbolics provided a successor to Flavors called New Flavors. Later Symbolics also supported Common Lisp and the Common Lisp Object System. Then Symbolics Common Lisp became the default Lisp dialect for writing software with Genera. The software of the operating system was written mostly in Lisp Machine Lisp (called ZetaLisp) and Symbolics Common Lisp. These Lisp dialects are both provided by Genera. Also parts of the software was using either Flavors, New Flavors and Common Lisp Object System. Some of the older parts of the Genera operating system have been rewritten in Symbolics Common Lisp and the Common Lisp Object system. Many parts of the operating systems remained written in ZetaLisp and Flavors (or New Flavors).
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