What are the common storage devices?

The only difference between volatile memory and nonvolatile memory is that the power-off data of the former will be cleared.

1, the representative of volatile memory is RAM, which is divided into DRAM (Dynamic Random Access Memory) and s RAM (Static Random Access Memory). The difference between them lies in the production process. SRAM latches data through transistors, while DRAM charges data through capacitors. SRAM technology is complex and the production cost is high, so we all choose DRAM as expensive large-capacity RAM. And SRAM is faster.

2. Since RAM is a memory, it is necessary to transmit data, and transmitting data is communication. Communication is divided into synchronous communication and asynchronous communication. The DRAM and SRAM we mentioned earlier are asynchronous communication, which is not as fast as SDRAM and SSRAM. So now the large-capacity RAM memory is SDRAM. Synchronization synchronization

3. Now the memory chip used in computer is RAM. My computer desktop uses DDR3SDRAM, my mobile phone uses DDR4 SDRAM, and the embedded development board uses DDR2 SDRAM. Then the difference between DDR SDRAM and SDRAM lies in the double rate (double data rate) of DDR. SDRAM only represents one data of the rising edge of the clock, while DDR SDRAM can represent one data of both the rising edge and the falling edge. DDR is also improved step by step, including the first generation, the second generation, the third generation, and now there are four generations.

4. Cache is very common in CPU, which belongs to SRAM in essence, so it is expensive, but faster than dram. In computer, the cache (sram) is faster than the memory (DRAM), so the cache is the bridge between CPU and memory.

5. So how does cache speed up the communication between CPU and memory? Understand that the contradiction between CPU and memory cache should be solved first. Paradoxically, the CPU reads very fast, but the speed given by the memory is very slow, so the CPU has to pick up the data for a while and wait for a while, which wastes the processing time of the CPU. We put the data in the memory that the CPU often reads into the cache, and the CPU reads the cache quickly, so that the CPU avoids the waiting time and improves the processing speed of the CPU. Another question is how does cache know which data is commonly used by CPU? In fact, cache stores a part of data that PU has just used or recycled, that is, caches a part of data. So caching is also called caching.

6. Common nonvolatile memories include ROM, FLASH, CD, floppy disk and mechanical hard disk. They have the same function, but the implementation process is different.

7. CDs, floppy disks and mechanical hard disks are all easy to understand, so I won't explain them.

8.ROM (read-only memory) used to be read-only, that is to say, this kind of memory can only read the data inside, but can't write the data. In fact, it is not easy to write data into memory before, so this kind of memory is made by the manufacturer and cannot be modified later. Now that the technology is mature, ROM can also write data, but the name is reserved.

9.ROM is divided into mask ROM, OTPROM, EPROM and EEPROM. The mask ROM is a mask ROM. Once it is produced by the manufacturer, users cannot change the data in it. OTPROM (one-time programmable read-only memory) can be turned into one memory at a time. After leaving the factory, users can only write data once, and then they can't modify it. Usually, it is used as a storage key. EPROM(Easerable programmable ROM) can be erased and written many times. But it needs to be erased under ultraviolet light in a specific environment, so this kind of memory is not convenient to write. EEPROM (Electrically Erasable Programmable ROM) is now widely used because data can be erased and written as long as there is electricity.

10, FLASH is a kind of memory that can be read and written, called FLASH, and FLASH is also called flash ROM. Some people regard Flash as ROM. Compared with EEPROM, FLASH has a large storage capacity. FLASH is faster than the current mechanical hard disk, and the current U disk and SSD solid-state hard disk are Nandflash. FLASH is divided into Norflash and Nandflash.