Memory Type Analysis

Document directory

• SRAM
• DRAM
• Prom
• EPROM
• EEPROM

I recently used several types of memory, but it will always be mixed up. So I found the characteristics of various types of memory on the Internet and sorted it out for future use.

Memory by purpose can be divided into external memory and internal memory. External Storage is usually a magnetic medium or a CD, which can store information for a long time. Memory refers to the storage part on the motherboard. It is used to store the currently running data and programs. It is only used to temporarily store programs and data. If the power is off or power is down, data will be lost.

Ram

Ram(Random access memory ). The content of a storage unit can be retrieved or stored as needed, and the access speed is irrelevant to the location of the storage unit. This type of storage will lose its storage content when the power is down, so it is mainly used to store programs that are used for a short time. According to different storage information, random memory is divided into static random memory (static RAM, SRAM) and dynamic random memory (Dynamic RAM, Dram ).

 

SRAM

SRAM(Static RAM, static random memory), no need to refresh the circuit, data will not be lost, and, generally, it is not the use of row and column addresses. However, its integration is relatively low, and it is not suitable for memory with large capacity. It is generally used in the cache of the processor. Like the S3C2440 arm9-processor, 4 k sram is used for CPU startup.

SRAM is actually a very important type of memory, which is widely used. The speed of SRAM is very fast, and data integrity can be maintained during fast reading and refreshing. The internal structure of the SRAM uses a bi-stable circuit to store data. The circuit structure of SRAM is very complex. Creating an SRAM of the same capacity is much more costly than dram. That is why it restricts its development. Therefore, SRAM is only used for the level-1 cache inside the CPU and the built-in level-2 cache. Only a small number of network servers and routers can use SRAM.

 

DRAM

Dynamic RAM, dynamic random access to memory, data needs to be refreshed once every time to save the data. In addition, the row and column addresses are reused, and many of them have the page mode. SDRAM is one of them.

 

SDRAM

SDRAM(Synchronous DRAM, synchronous dynamic random memory), that is, Data Reading and Writing requires clock synchronization. Its storage units are not linearly arranged, but paging.

DRAM and SDRAM have a large capacity due to technical issues. However, the read/write speed is not as high as that of SRAM.

In general embedded productsMemoryAll use the SDRAM. ComputerMemoryRam is also used, called ddr sdram, which has a high degree of integration. Because it is dynamic, a refresh circuit is required and data must be refreshed at intervals.

 

Rom

Read-only memory, a general term for read-only memory.

In the early stages of development, BIOS was stored in ROM (read-only memory. The internal data of Rom is burned in the manufacturing process of Rom. The content of ROM can only be read but cannot be modified, the user can only verify that the written data is correct and cannot make any modifications. If you find any errors in the information, you only need to discard it and make a new order. Rom is produced on the production line. Due to the high cost, it is generally used only in mass applications.

 

Prom

Programmable read-only memory can only be written once. If it is wrong, it has to be decommissioned. Now it is seldom used. It seems that the memory is used in the OPT single-chip microcomputer with lower costs.

 

EPROM

EPROM(Erasable Programmable Rom,Erasable Programmable RomThe chip can be erased and written repeatedly, solving the drawback that the PROM chip can only be written once.

The EPROM chip has an obvious feature. In its ceramic encapsulation, a glass window is opened. Through this window, you can see its internal integrated circuit, the ultraviolet rays can reach the internal chip through this hole to erase the data in it. To complete the chip erasure operation, the EPROM eraser is used.

A dedicated programmer is used to write data in the EPROM, and a certain programming voltage (VPP = 12-24 V, depending on the chip model ). The EPROM model starts with 27. For example, 27c020 (8*256 K) is an EPROM chip with 2 m bits capacity. After the EPROM chip writes data, it also needs to block the window with an opaque sticker or tape to avoid damage to the data caused by ultraviolet radiation. When the EPROM chip is in the blank state (after being erased with UV light), the data of each internal storage unit is 1 (high level ).

 

EEPROM

EEPROM(Electrically Erasable Programmable Rom,Electrically erasable programmable read-only memory), A storage chip with no data loss after power loss. The EEPROM is a user-changeable read-only memory that can be erased and re-programmed (rewritten) by a voltage higher than normal ), that is, you can erase existing information on your computer or on a dedicated device and re-program it. Unlike the EPROM chip, the EEPROM can be modified without needing to be taken out from the computer. It uses a lot of memory, such as the 24cxx series EEPROM.

In an EEPROM, when the computer is used, it can be re-programmed frequently. the lifetime of the EEPROM is an important design consideration parameter.

One special form of EEPROM isFlash MemoryThe application is usually the voltage in the PC to erase and re-program.

EEPROM is generally used for plug-and-play (Plug & play). It is often used in interface cards to store hardware settings data, and is also commonly used in "Hardware locks" to prevent illegal copying of software.

 

Flash)

Flash memory is a non-volatile memory, that is, data will not be lost when the power is down. Because flash memory does not rewrite data in bytes like Ram (Random Access Memory), it cannot replace Ram.

Flash cards use flash memory technology to store electronic information. They are generally used as storage media in small digital products such as digital cameras, handheld computers, and MP3, so it looks like a card, so it's called a flash card. Depending on different manufacturers and applications, flash cards may include USB flash drives, smartmedia (smcard), compact flash (CF card), multimediacard (mmccard), and secure digital (SD card) memory stick, XD-Picture Card, and microdrive ). Although these flash cards have different appearances and specifications, their technical principles are the same.

 

Both NAND Flash and nor Flash are currently using a lot of non-volatile flash.

Flash flash memory is a non-loss-prone memory. It can be used to erase and re-program memory unit blocks called blocks. Write operations on any flash device can only be performed in an empty or erased unit. In most cases, the flash device must be erased before writing. It is very easy for the NAND device to perform the erasure operation, and nor requires that all the bits in the target block be written to 0 before the erasure.

Since the nor device is erased with 64 ~ For blocks of KB, the time for performing a write/erase operation is 5 S. In contrast, the erased NAND device is 8 ~ For 32 KB blocks, it takes up to 4 ms to perform the same operation.

When the block size is erased, the performance gap between nor and nadn is further extended. Statistics show that, for a given set of write operations (especially when updating small files, more erasure operations must be performed in the nor-based unit. In this way, when selecting a storage solution, the designer must weigh the following factors.

● Nor reads faster than NAND.

● NAND writes much faster than nor.

● NAND's 4 Ms erasure speed is far faster than nor's 5s.

● Most write operations require erasure first.

● NAND has fewer erased units and fewer erased circuits.

Nor Flash has an SRAM interface and enough address pins to address it, so it can easily access every byte in it.

Nand devices use complex I/O ports to access data in a serial manner. Different products or vendors may use different methods. Eight pins are used to transmit control, address, and data information.

Nand read and write operations use 512 bytes of blocks, which is a bit like hard disk management. Naturally, NAND-based memory can replace hard disks or other Block devices.

Simply put, in a computer,Ram,RomAll are data storage. Ram is a random access memory, which is characterized by volatile power loss and memory loss. Rom usually refers to the fixed memory (one write, repeated read), which features the opposite of RAM.

RomAnd once curing (Prom), Optical Erasure (EPROM) And Erasure (EEPROM) Rewrite several types. For example, if a sudden power failure or a file is disabled if it is not saved, the ROM can randomly Save the files that have not been stored, But Ram will remove the files that have not been saved.

RamStatic random storage (SRAMAnd dynamic random memory (DRAM).