Transmited light micrograph of a synchronous dynamic random-access memory (SDRAM) module (capacity 128 MB, PC-100 serie). Random-access technology allows the CPU to read and write data very quickly. The information therein is accessed randomly. This addressable semiconductor memory device of solid-state volatile memory synchronizes itself with the CPU clock, reaching a high data access rate. Organized into several million memory cells (a capacitor and a transistor per unit), each one may store a binary digit, or bit. To preserve the information, a periodic refresh of written data is required. Nevertheless, the chip can reach very high densities of storage and is therefore generally used as the main memory in personal computers. It is by far the most widely used RAM. Field of view size: 198 x 297 痠 (0.008 x 0.012 in)