Sun Microsystems has announced that Solaris 10 has surpassed four million registered licences, two thirds of which are on x86 systems, exactly one year after the operating system's initial release. 

Solaris 10 is part of the Solaris Enterprise System, which also contains the Sun Java Enterprise System (Java ES), Sun N1 system manager software and Sun Studio software developer tools.

The company announced recently that the Java ES surpassed one million subscriptions in two years.

Tom Goguen, vice president of software marketing at Sun, said: "Sun has made Solaris 10 available for free, has started supporting it on more than 500 x86 systems including HP and IBM, and has open sourced the software."

In a parallel announcement Sun also unveiled services in conjunction with its partners to provide tools and support for customers wanting to migrate proprietary data centre environments to Solaris 10.