Hard drives and data storage banks are kept in server rooms, while servers and printers are kept in computer rooms. Because these two rooms are so different, they require distinct cooling methods. They have a propensity to overheat, which is why a conditioning unit designed for that space is essential. The power supply in a server room must be capable of delivering sufficient electricity to the other equipment in the room as well as to the server itself. Therefore, it needs to be able to handle high electrical loads with low voltage drops across its components. These factors mean that server power supplies tend to be large and use many heavy-duty components such as transformers and capacitors. They also need reliable cooling to keep them from overheating. Server rooms typically have one or more air conditioners or heat pumps for heating and cooling. This is because they go through cycles of heating and cooling several times during the day. Heating in the winter and air-conditioning in the summer are both forms of thermal management. The amount of energy used by equipment in a server room can rise dramatically when not cooled properly. Excess heat can cause components to fail or damage other equipment in the room. A failed or damaged component may need to be replaced, increasing the cost of ownership. Cooling systems also consume energy, so reducing the demand on them using proper thermostats can save money. Server rooms are usually well-lit for ease of use.