concept
The semiconductor memory is a semiconductor device capable of storing a large amount of binary information.
ROM：
ROM. ROM can only read data, not quick to modify or rewrite data. ROM advantage of simple circuit configuration, and data is not lost after the power failure. The disadvantage is only applicable to those occasions storage of fixed data.
PROM: only be modified once
ERPOM: ultraviolet erasable
EEPROM: Electrically Erasable
T2: is the storage tube, T1: gating tube. The floating gate has a negative charge is not charged in the state 0 or 1 to distinguish.
Flash: Electrically Erasable
Writing principle: avalanche breakdown, electrons pass through the oxide layer to the floating gate layer.
RAM：
Random access memory; works depending on the memory cell employed, in turn divided into a random access memory, static random memory (SRAM) and dynamic memory (DRAM). Since the structure is very simple dynamic memory, so it can reach much higher than the degree of integration of a static memory.
Advantages: easy to read and write, the use of flexible.
SRAM:
Central storage for the SR latch, for memorizing a binary code. Plus two gated switches total of six N-channel enhancement-type MOS transistor
DRAM：
Since the leakage capacitance, it is necessary to charge the capacitor in a certain time. --- dynamic refresh said.