What is the difference between ROM, ram and flash? SRAM、DRAM、PROM、EPROM、EEPROM

ROM、RAM and FLASH What's the difference ？

SRAM、DRAM、PROM、EPROM、EEPROM

One . Performance comparison

1.ROM and RAM 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 .

• ROM yes Read Only Memory（ read-only memory ） Abbreviation , The data inside can only be read during normal application , Can't write , Storage speed is not as fast as RAM;

• RAM yes Random Access Memory（ Random access memory ） Abbreviation , It is called ram because ： When the RAM When reading or writing data , The time spent is independent of the location where the message is located or where it is written .

2.RAM There are two main categories ：SRAM and DRAM.

• SRAM It's static RAM(Static RAM/SRAM), Static means that there is no need to refresh the circuit , Data will not be lost ,SRAM Very fast , It is currently the fastest reading and writing storage device , But it's also very expensive , So it's only used in very demanding places , for example CPU One level buffer for , Secondary buffering .

• DRAM For the dynamic RAM(Dynamic RAM/DRAM), Dynamic means to refresh data every once in a while , To save the data ,DRAM The time to keep the data is short , It's faster than SRAM slow , But it's better than any ROM Be quick , But in terms of price DRAM comparison SRAM It's much cheaper , Computer memory is DRAM Of .RAM Compare the price with ROM and FLASH higher .

  • SDRAM It's synchronization （S refer to synchronous）DRAM, Synchronization means that the memory needs to synchronize the clock , Internal command transmission and data transmission are based on it .SDRAM There's a synchronization interface , Wait for a clock signal before responding to control input , In this way, we can communicate with the computer The system bus Sync ;
  • DDR、DDR2、DDR3 All belong to SDRAM,DDR yes Double DateRate It means , Three refers to three generations of the same series , Faster , More capacity , Less power consumption , Now it's out DDR4, It's the same series .

NVRAM（ Non-Volatile Random Access Memory） Is a nonvolatile random access memory , It refers to a kind of data that can still be maintained after power failure RAM.

3.ROM It is divided into PROM、EPROM、EEPROM

• PROM：（P Refers to Programmable） A programmable ROM, According to the needs of users , To write content , But only once , It can't be changed any more ;
• EPROM：Erasable Programmable（ Erasable programmable ）,PROM Upgraded version , It can be programmed many times , Only use ultraviolet light to erase ;
• EEPROM：Electrically Erasable Programmable（ Electrically erasable programmable ） Upgraded version , It can be programmed many times , Use electrical erasure .

4.FLASH Memory is also called flash memory , Power down without losing data , Large capacity , Cheapness .

It is a combination of ROM and RAM Strengths , Not only electronically erasable and programmable （EEPROM） Performance of , It doesn't lose data when power is off, and it can read data quickly （NVRAM The advantages of ）,U Plate and MP3 It's this kind of memory .

It is divided into NAND FLASH and NOR FLASH,

• NOR FLASH Read speed ratio NAND FLASH fast , But the capacity is not as good as NAND FLASH, The price is also higher ,
• however NOR FLASH It can be executed in the chip , The sample application can be directly in flash Running in flash memory , You don't have to read the code into the system RAM in .NANDFLASH More dense , It can be used as the storage of big data .

Two . Price comparison

RAM Compare the price with ROM and FLASH higher .

3、 ... and . Capacity comparison

RAM The capacity of is the minimum ratio ROM and FLASH Relatively small capacity ,RAM It is characterized by being readable and writable , After powering off the memory , The data stored in it will be lost . We often talk about memory , Such as computer memory , The memory of the phone , Include CPU Cache used in , All belong to RAM This type of memory .

ROM and FLASH Capacity ratio RAM The capacity of is relatively large . Generally, one is customized ROM Modifying the system version information is all in this .（system） Is the directory where the system is located , amount to PC Systematic Windows Folder ,（boot.img） It's a mirror file , It's called the kernel , General transplantation ROM It will be used .

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