automobile's internal combustion engine, with the water being circulated by a water pump through a water block mounted on the CPU (and sometimes additional components as GPU and northbridge) and out to a heat exchanger, typically a radiator. The radiator is itself usually cooled additionally by means of a fan. Besides a fan, it could possibly also be cooled by other means, such as a Peltier cooler (although Peltier elements are most commonly placed directly on top of the hardware to be cooled, and the coolant is used to conduct the heat away from the hot side of the Peltier element). A coolant reservoir is often also connected to the system. Besides active liquid cooling systems, passive liquid cooling systems are also sometimes used. These systems often leave out a fan or a water pump, theoretically increasing their reliability and making them quieter than active systems. The downsides of these systems are that they are much less efficient in discarding the heat and thus also need to have much more coolantand thus a much bigger coolant reservoirgiving the coolant more time to cool down. Liquids allow the transfer of more heat from the parts being cooled than air, making liquid cooling suitable for overclocking and high performance computer applications. Compared to air cooling, liquid cooling is also influenced less by the ambient temperature. Liquid cooling's comparatively low noise-level compares favorably to that of air cooling, which can become quite noisy. Disadvantages of liquid cooling include complexity and the potential for a coolant leak. Leaking water (and any additives in the water) can damage electronic components with which it comes into contact, and the need to test for and repair leaks makes for more complex and less reliable installations. (The first major foray into the field of liquid-cooled personal computers for general use, the high-end versions of Apple's Power Mac G5, was ultimately doomed by a propensity for coolant leaks.) An air-cooled heatsink is generally much simpler to build, install, and maintain than a water cooling solution, although CPU-specific water cooling kits can also be found, which may be just as easy to install as an air cooler. These are not limited to CPUs, and liquid cooling of GPU cards is also possible. While originally limited to mainframe computers, liquid cooling has become a practice largely associated with overclocking in the form of either manufactured all-in-one (AIO) kits or do-it-yourself setups