A form of memory that is relatively inexpensive to manufacture; but, by its nature, requires constant updating unless data stored in it is lost. (Data in each memory location is maintained by a capacitor which only holds a charge for a short time. This charge must be refreshed frequently.)

The first commercial DRAM chip (Intel 1103) was introduced in 1970. Early chips stored up to 16Kbits. Multiple chips were needed to accommodate storage of data bytes as each byte consists of eight bits plus an error correcting bit.

Surface mounting of chips began with 256Kbit DRAM. This, and other improvements, reduced the size of DRAM components. More recently, chips are all mounted onto modules which plug into memory slots in the computer. The modules include the Single In-line Pin Module (SIP), Single In-line Memory Module (SIMM), and Dual In-line Memory Module (DIMM).

DRAMs are constructed with arrays of rows and columns; data being stored at the intersections. Data is read by reading out all bits in a row to a buffer (disharging the storage capacitors in the process). The required datum or data is read from the buffer and the bits are then written back out to the storage row (refreshing the storage capacitors). If data in a particular row has not been read and refreshed before the capacitors need to be refreshed then that row must be refreshed by the controller. Refresh rates vary with the construction of the DRAM but have typically tended toward 16 microseconds or so.