ABSTRACT
Outwardly, DRAMs and SRAMs differ little, except in their relative density and performance. But
internally, DRAMs are distinguished from SRAMs, in that no bi-stable electronic circuit maintains the
information. Instead, DRAM information is stored ‘‘dynamically’’ as charge on a capacitor. Modern designs
feature one field-effect transistor (FET) to access the information for both reading and writing and a thin
film capacitor to store information. SRAMs maintain their bi-stability, as long as power is applied, through a
cross-coupled pair of inverters within each storage cell. Almost always, two additional transistors access the
internal nodes for reading and writing. Most modern cell designs are CMOS, with two P-channel and four
N-channel FETs.
