A software version is a code attached to a particular release of software to distinguish it from other releases of the same software.

Decimal

The most common software versioning scheme is a plain decimal scheme, in which different major releases of the software each receive a unique number. An example of this is MS-DOS, which had seven major versions and used numbers 1 through 7 to denote them. Usually, software using this numbering scheme also includes a minor version number after the major version number to record smaller changes between releases. For example, MS-DOS released version 3.3 in April 1987, after versions 3.0, 3.1 and 3.2 had been released, but before MS-DOS version 4.0 was released in June 1988.

Software which carries decimal version numbers before 1.0 is usually in an "alpha" or "beta" state (see below). v. is often used as an abbreviation for "version", for example "MS-DOS v. 3.3". Often the "v." or "version" is omitted completely.

Some software packages use more advanced versions of the decimal numbering scheme, such as Linux, which uses odd minor version numbers to denote development releases and even minor version numbers to denote stable releases. For example, Linux 2.5 was a development family of the second major design of the Linux kernel, and Linux 2.6 was the stable release family that Linux 2.5 matured into. After the minor version number in the Linux kernel is the release number, in ascending order; for example, Linux 2.4.0 -> Linux 2.4.22. Even further, a trivial version number was added to 2.6.8, making 2.6.8.1 which denoted a very minor change.

Date

The WINE project uses a date versioning scheme, which uses the year followed by the month followed by the day of the release; for example, "WINE 20040505". This is intended to lead into a decimal versioning scheme when WINE 1.0 is released, but assists in keeping track of the large number of development WINE releases until then.

Other schemes

Some software producers use different schemes to denote releases of their software. For example, the Microsoft Windows operating system was first labelled with major/minor version numbers (Windows 3.11), then by years (Windows 95, Windows 98, Windows 2000), and also by code names (Windows Me, Windows XP). The Debian project uses a major/minor versioning scheme for releases of its operating system, but uses code names from the movie Toy Story during development to refer to stable, unstable and testing releases.

Alpha and beta software

Programs that are very early in development are often called "alpha" software, after the first letter in the Greek alphabet. After they mature but are not yet ready for release, they may be called "beta" software, after the second letter in the Greek alphabet.

In general, the version of a product is considered to be alpha if it is feature incomplete; that is, all of its functions have not been implemented by the developer at the time. It is considered to be beta when all the features have been implemented but have not been tested. As a result, the practice of testing finished software for computer bugs is often known as "beta testing."

Release candidates

Software packages which are soon to be released as a particular version may carry that version tag followed by "rc-#", indicating the number of the release candidate. When the version is actually released, the "rc" tag disappears.

Unusual versioning schemes

TeX has an idiosyncratic version numbering system. Since version 3, updates have been indicated by adding an extra digit at the end of the decimal, so that the version number asymptotically approaches π. The current version is 3.141592. This is a reflection of the fact that TeX is now very stable, and only minor updates are anticipated. Knuth has stated that the "absolutely final change (to be made after my death)" will be to change the version number to π, at which point all remaining bugs will become features.