Dynamic Random Access Memory
RAM memory circuits are classified into two main groups: dynamic memories (DRAM) or static memories (SRAM).
Dynamic memories use tiny capacitors to store data. Since capacitors lose automatically lose their charge after some time it is necessary to recharge these capacitors from time to time. This recharge cycle is called refresh.
Static memories use circuits called flip-flops to store data. These circuits are far bigger than capacitors, however they are faster and don’t need a refresh cycle.
Static memories are faster than dynamic memories, but their power consumption is higher (thus more heat is created), they are physically bigger and are more expensive.
On the PC the main RAM memory use dynamic memory circuits. Static memories are used in a circuit called memory cache, which nowadays is located inside the computer processor.
Dynamic memories can be manufactured using several different technologies such as FPM, EDO, SDRAM, DDR-SDRAM, etc.