KDE 3 was much larger than the previous series, consisting of six major releases. The API changes between KDE 2 and KDE 3 were comparatively minor, meaning that the KDE 3 can be seen as largely a continuation of the KDE 2 series. All releases of KDE 3 are built upon Qt 3, which was only released under the GPL for Linux and Unix-like operating systems, including Mac OS X. For that reason, KDE 3 is only available on Windows through ports involving an X server.