/XCL eXtends Clock Limits for official AMD overclocking APIs. Which means that it also extends clock limits for CCC or any other other vendor specific tool using official overclocking interfaces provided by AMD. Considering that it is using official AMD overclocking interface, it is compatible with ULPS. This method is equal to flashing new VGA BIOS with extended Overdrive clock limits. However, this method uses hidded VGA BIOS emulation debug feature of Catalyst driver. Once AMD decide to remove it from driver, it will stop working. It is also necessary to re-extend clock limit after driver re-installation because VGA bios emulator resides in Catalyst registry entries. Unofficial overclocking uses old undocumented "hole" in AMD driver, which allows to re-program PowerPlay table and bypass Overdrive clock limits. AMD used this unofficial interface in the past for their internal AMDGPUClockTool. Currently the "hole" is not supported by AMD in any way, it is incompatible with some AMDs own power saving technologies (ULPS), it has many side effects due to "nice" AMD programming skills (such as resetting fan speed and powertune to defaults, etc, etc).