Qt 4 is available under the LGPL for Mac OS X and Windows, which allows KDE 4 to run on those platforms. However, tests reveal that KDE 4.4 has the highest memory utilization on default Ubuntu installations when compared to GNOME 2.29, Xfce 4.6, and LXDE 0.5. The KDE libraries themselves have also been made more efficient. The port to the Qt 4 series was expected to enable KDE 4 to use less memory and be noticeably faster than KDE 3. This is a short overview of major changes in KDE Software Compilation 4. Versions 4.0 to 4.3 of KDE Software Compilation were known simply as KDE 4 – the name change was a component of the KDE project's re-branding to reflect KDE's increased scope. This was made possible by the port to Qt 4, which facilitated support for non- X11-based platforms, including Microsoft Windows and Mac OS X. One of the overall goals of KDE Platform 4 was to make it easy for KDE applications to be portable to different operating systems. It also included a new, unified desktop and panel user interface called Plasma, which supported desktop widgets, replacing K Desktop Environment 3's separate components. It contained a new multimedia API, called Phonon, a device integration framework called Solid and a new style guide and default icon set called Oxygen. The series included updates to several of the KDE Platform's core components, notably a port to Qt 4.

Major releases (4.x) were released every six months, while minor bugfix releases (4.x.y) were released monthly. Following KDE SC 4, the compilation was broken up into basic framework libraries, desktop environment and applications, which are termed KDE Frameworks 5, KDE Plasma 5 and KDE Applications, respectively. It was the follow-up to K Desktop Environment 3. KDE Software Compilation 4 ( KDE SC 4) was the only series of the so-called KDE Software Compilation (short: KDE SC), first released in January 2008 and the last release being 4.14.3 released in November 2014. GPL, LGPL, BSD license, MIT license and X11 license Whole desktop: Unix-like with X11 and also Windows XP– 7.

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