Each release of Simics has a unique three digit version number, e.g. 2.2.7. A change in the first or second number is defined as a major release. Changing the third number is a minor release. Major releases are generally distributed to provide significant product improvements. Minor releases are generally distributed when adding new simulation models or for error corrections.
A release with an odd second number or with a letter in the version e.g. 2.3.2 or 3.1b.0 is a development release and is not subject to any support commitment. Development releases are generally distributed to provide early access to new functionality.