RAM, ROM, SRAM, DRAM, SSRAM, SDRAM, FLASH, EEPROM

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RAM, ROM, SRAM, DRAM, SSRAM, SDRAM, FLASH, EEPROM [Copy link]

RAM (Random Access Memory) Random Access Memory. The contents of a storage unit can be taken out or stored at will as needed, and the access speed is independent of the location of the storage unit. This type of memory will lose its storage content when the power is off, so it is mainly used to store programs used for a short time. According to the different information stored, random access memory is divided into static random access memory (Static RAM, SRAM) and dynamic random access memory (Dynamic RAM, DRAM). ROM (Read-Only Memory) is a solid-state semiconductor memory that can only read out previously stored data. Its characteristic is that once the data is stored, it cannot be changed or deleted. It is usually used in electronic or computer systems that do not need to change data frequently, and the data will not disappear when the power is turned off. SRAM (Static RAM) can save the data stored inside it without refreshing the circuit. DRAM (Dynamic RAM) needs to be refreshed and charged once every period of time, otherwise the internal data will disappear. Therefore, SRAM has higher performance, but SRAM also has its disadvantages, that is, its integration is low. The same capacity of DRAM memory can be designed to be smaller, but SRAM requires a large volume and consumes more power. Therefore, SRAM memory will occupy a part of the area on the motherboard. SRAM has high speed and good performance. It is mainly used in the following applications: 1) High-speed cache between CPU and main memory. 2) L1/L2 or external L2 cache inside CPU. SSRAM (Synchronous SRAM) is synchronous static random access memory. Synchronous means that the memory needs a synchronous clock to work, and the internal command sending and data transmission are based on it; random means that the data is not stored linearly in sequence, but is read and written by the specified address. All accesses to SSRAM are started at the rising/falling edge of the clock. The address, data input and other control signals are all related to the clock signal. This is different from asynchronous SRAM. The access of asynchronous SRAM is independent of the clock, and the data input and output are controlled by the change of the address. SDRAM (Synchronous DRAM) is synchronous dynamic random access memory. Synchronous means that the memory needs a synchronous clock to work, and the internal command sending and data transmission are based on it; dynamic means that the storage array needs to be constantly refreshed to ensure that the data is not lost; random means that the data is not stored linearly in sequence, but is read and written at a freely specified address. MRAM: DRAM's replacement FLASH is flash memory. It is a long-life non-volatile memory (it can still keep the stored data information when the power is off). Data deletion is not in units of single bytes but in fixed blocks (Note: NOR Flash is written and stored as bytes.), and the block size is generally 256KB to 20MB. { NandFlash and NorFlash are both a type of Flash, both are scattered storage, and both are disk storage mesons, but NandFlash is generally larger, while NorFlash is smaller, and NorFlash is more expensive, and NorFlash writes slower, but reads faster, while NandFlash reads slower and writes slower} EEPROM is electronically erasable read-only memory. EEPROM is different from flash memory in that it can be deleted and rewritten at the byte level instead of erasing the entire chip, so that flash memory can be updated faster than EEPROM. Because it can still save data when the power is off, flash memory is usually used to save setting information, such as saving data in the computer's BIOS (basic input and output program), PDA (personal digital assistant), digital camera, etc. * Serial EEPROM (I2C http://blog.csdn.net/kala111/article/details/50965051 / SPI) * Parallel EEPROM [Flash is divided into bus flash and SPI flash according to the interface. Bus flash requires an external bus interface on your MCU, and SPI flash reads and writes flash through the SPI port. In terms of speed, bus flash is faster than SPI, but SPI is cheaper. ]