DRAM modules are collections of dynamic random access memory (DRAM) chips assembled on circuit boards. DRAM chips are single-transistor dynamic memory cells that use capacitors to store each bit in a row-and-column addressable format. DRAM chips are a type of random access memory (RAM) that requires the capacitor to be continually charged or refreshed to retain data. Because a DRAM module is a dynamic memory device, it requires a power supply to maintain its data. In this way, DRAM modules use volatile memory. By contrast, static memory does not require the capacitor to be refreshed. Flash memory retains data regardless of the power supply.