Static RAM
Each cell in a static RAM is implemented using a flip flop which is implemented using several MSOFET transistors. External power is required to operate the transistor. As long as, the external power is applied, the static memory cell retains the data. The circuit of a single flip flop based cell which can store a binary 0 and 1 is shown;
Figure: Static cell based on a flip flop
Dynamic RAM
In dynamic RAM, a single memory cell is therefore, implemented using a single transistor and a capacitor which occupy lesser space as compared to six transistor which are used to implement a single static cell. Therefore, the density of capacitor based memory is significantly increased. The capacitor based memory is known as dynamic RAM (DRAM). The circuit diagram of a single DRAM capacitor based memory cell is shown;
Figure: Writing a 1 or 0 into the DRAM cell
Figure: Reading a 1 or 0 from DRAM cell
Figure: Refreshing a DRAM cell
Mask ROM
The storage cell in a mask ROM is implemented using a MOS transistor. The structure of a storage cell in a mask ROM is shown;
Figure: Cell storing a logic 1 or logic 0
Flash Memory
The high density flash memory cell is implemented using a single floating gate MOS transistor.
Figure: Programming with logic 0 and logic 1
Figure: Read operation to read logic 0 and logic 1
Figure: Erase operation of the FLASH memory cell
