RAM, computer main memory in which specific contents can be accessed (read or written) directly by the central processing unit in a very short time regardless of the sequence (and hence location) in which they were recorded. Two types of memory are possible with random-access circuits: static RAM (SRAM) and dynamic RAM (DRAM). A single memory chip is made up of several million memory cells. In a SRAM chip each memory cell stores a binary digit (1 or 0) for as long as power is supplied. In a DRAM chip the charge on individual memory cells must be refreshed periodically in order to retain data. Because it has fewer components, DRAM requires less chip area than SRAM. Hence, a DRAM chip can hold more memory, though its access time is slower.