Classification of ram and ROM storage media

Storage media overview

1 executive summary

Common storage media are ram as well as rom;

 

storage medium

1.1 RAM

Ram , And cpu Internal storage for direct exchange of data , Also called memory ; Power failure does not save data ;

common ： Cell phone memory , Computer memory ;

1.2 ROM

Read only memory ; Internal data can only be read , It can't be modified ;

It is only used in mass production ;

1.3 The difference between the two

RAM and ROM It's all semiconductor memory ,ROM Data can still be maintained when the system is powered off , and RAM Usually, data is lost after power failure , Typical RAM It's the memory of the computer .

2 RAM

2.1 SRAM：

（static ram/sram）

It is the fastest memory at present , The price is very expensive ; Use in cpu Of 1 level 2 level cache（ buffer ） On , On power , Data will not be lost ; No need to constantly refresh ;

2.2 DRAM

（dynamic ram/dram）

Dynamic memory ; At present, the memory used by calculators is dram;dram The storage speed of is not sram fast , But compared to rom It's much faster ;

It needs to be refreshed constantly when the power is on , To save the data ; And it's column address multiplexing , Many have page mode ;

2.2.1 SDRAM

Synchronous dynamic memory , Data reading and writing requires a clock to synchronize .

2.2.2 DDR RAM

（date-rate ram）

It's also called ddr sdram, One clock cycle can read and write data twice ;

2.2.3 wait

There are many other common DRAM;

3 ROM

3.1 PROM

Programmable read only memory , Only one write is allowed , In fact, that is “ Once programmable read only memory ”

 

3.2 EPROM

Erasable programmable read only memory ; Erasable , After erasing, you can write again ; The method of erasing is troublesome , Need to use ultraviolet radiation for a period of time

3.3 EEPROM

Point solution erasable and programmable read-only register ;

common ：28377 Control chip , The saved control parameters are generated by the external eeprom To achieve ;

 

3.4 FLASH MEMORY

Flash memory , Power down to save

There are common ：u disc , Hard disk , Board mounted on-board flash, Off slice flash

3.4.1 NOR FLASH

nor flash Read and sdram It's the same , Users can run the installation directly nor flash The code in .

3.4.2 NADN FLASH

nadn flash There's no random access to memory , The reading method is to read one piece at a time （ Usually once 512 byte ）;

Users cannot run directly nadn flash The code on

3.4.3 Restatement

nor flash Because its reading speed is very fast , It is generally used to store operating system and other information ;

nadn flash The most common application is , The design of embedded system DOC（disk on chip）