What is the difference between Rom, Ram, DRAM, SRAM and flash.

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Rom and RAM are both semiconductor memory, Rom is short for read only memory, and Ram is short for random access memory. ROM can still maintain data when the system stops power supply, while Ram usually loses data after power loss. A typical Ram is the computer memory.


Ram has two categories: static RAM (static RAM/SRAM). The speed of SRAM is very fast. It is the fastest storage device for reading and writing, but it is also very expensive, therefore, it can only be used in demanding scenarios, such as CPU Level 1 buffering and level 2 buffering. The other is dynamic RAM (Dynamic RAM/Dram). DRAM retains data for a short period of time and is slower than SRAM, but it is faster than any Rom, but in terms of price, DRAM is much cheaper than SRAM, and computer memory is dram.


DRAM is divided into many types. Common types include fpram/fastpage, edoram, SDRAM, ddr ram, RDRAM, sgram, and wram. Here we will introduce a ddr ram.


Ddr ram (date-rate RAM) is also called ddr sdram. The improved Ram is basically the same as that of SDRAM. The difference is that it can read and write data twice at a clock, this doubles the data transmission speed. This is the most widely used memory in computers, and it has a cost advantage. In fact, it beat Intel's other memory standard-Rambus DRAM. In many high-end graphics cards, high-speed ddr ram is also provided to increase the bandwidth, which can greatly improve the pixel rendering capability of the 3D accelerator card.


Memory Working principle:


Memory is used to store the data and programs currently in use (that is, execution). The memory of the computer we usually refer to dynamic memory (that is, Dram ), in dynamic memory, the so-called "dynamic" means that after we write data into dram, data will be lost after a period of time, so we need a memory refresh operation by using a peripheral circuit.


The specific working process is as follows: whether a dram storage unit stores 0 or 1 depends on whether the capacitor has a charge. If there is a charge, it indicates 1, and if there is no charge, it indicates 0. However, after a long period of time, the capacitance of 1 will be discharged, indicating that the capacitance of 0 will absorb the charge, which is the cause of data loss. The refresh operation regularly checks the capacitance, if the power is greater than 1/2 of the full power, it indicates 1 and the capacitor is fully charged. If the power is less than 1/2, it indicates 0 and the capacitor is discharged, to maintain data continuity.


There are also many types of Rom. The difference between the prom and the EPROM is that the prom is one-time, that is, after the software is filled in, it cannot be modified. This is an early product and cannot be used now. The EPROM is used to erase the original program through ultraviolet radiation and is a general memory. Another type of EEPROM is an electronic interface. It has a high price, a long write time, and a low write speed.


For example, the mobile phone software is usually placed in the EEPROM. When we call, some of the last dialing numbers are temporarily stored in the SRAM, rather than writing the pass record immediately (the call record is stored in the EEPROM ), at that time, there was a lot of important work (CALLS) to do. If you write data, a long wait would be unbearable for users.


Flash Memory, also known as flash memory, combines the strengths of ROM and Ram, not only has the electronic Erasable Programmable (EEPROM) performance, data will not be lost after power failure, and data can be quickly read (NVRAM advantage), which is used in USB flash drives and MP3. In the past 20 years, embedded systems have been using ROM (EPROM) as their storage devices. However, in recent years, Flash has completely replaced the position of RoM (EPROM) in embedded systems, it is used to store bootloader, operating system or program code, or directly used as a hard disk (USB flash disk ).


Currently, there are two types of FLASH: nor flash and nadn flash.


The reading of nor flash is the same as that of our common SDRAM. Users can directly run the code loaded in nor flash, which can reduce the capacity of SRAM and save costs.


NAND Flash does not adopt the random read Technology of memory. It reads a block at a time, usually 512 bytes at a time. Flash with this technology is cheaper. Users cannot directly run the code on NAND Flash. Therefore, many development boards that use NAND Flash use a small nor flash to run the startup code in addition to NAND flah.


Nor flash is usually used for small capacity. Because of its fast reading speed, it is used to store important information such as the operating system, while NAND Flash is used for large capacity, the most common nand flash application is the DOC (Disk On Chip) used in the embedded system and the "flash disk" we usually use, which can be erased online. Flash on the market is mainly from Intel, AMD, Fujitsu and toshba, while the main manufacturers of NAND Flash are Samsung and toshba.


Comparison between NAND Flash and nor flash


Nor and NAND are two major non-loss flash technologies on the market. Intel first developed nor Flash technology in 1988, which completely changed the previous situation where EPROM and EEPROM were integrated. Next, in 1989, Toshiba published the NAND Flash structure, emphasizing reducing the cost per bit and higher performance, and easily upgrading it through interfaces like disks. However, after more than a decade, a considerable number of hardware engineers are still confused about nor and NAND Flash.


Phase "Flash Memory" is often used with phase "nor memory. Many insiders do not know the advantages of NAND Flash compared with nor, because in most cases, Flash is only used to store a small amount of code, so nor flash is more suitable for some. Nand is an ideal solution for high data storage density.


Nor is the primary non-easy-to-lose Flash technology on the market. Nor is generally used to store a small amount of code. Nor is mainly used in the code storage media. Nor is characterized by simple application, no special interface circuit, and high transmission efficiency. It is an internal chip execution (xip, execute in place ), in this way, the application can run directly in the (NOR) flash memory without having to read the code into the system Ram. In 1 ~ The small size of 4 MB has high cost efficiency, but the low write and erase speeds greatly affect its performance. Nor Flash has an SRAM interface and enough address pins to address it, so it can easily access every byte in it. Nor flash occupies 1 ~ Most of the 16 MB flash memory market.


The NAND structure provides a very high unit density, achieves a high storage density, and writes and erases quickly. The difficulty of using NAND lies in Flash management and special system interfaces.


1. Performance Comparison:


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 1 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.


(Note: The erasure time of nor flash sector varies depending on the brand and size. For example, for 4 M Flash, some sector erasure times are 60 ms, while some require a maximum of 6 s .)


2. Interface differences:


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.


3. Capacity and cost:


The unit size of NAND Flash is almost half the size of the nor device. Because the production process is simpler, the NAND structure can provide a higher capacity within the given mold size, thus reducing the price accordingly.


Nor flash occupies 1 ~ Most of the 16 MB flash memory market, while NAND Flash is only used in 8 ~ Among the MB products, this also shows that nor is mainly used in code storage media. NAND is suitable for data storage. NAND shares the largest share in the compactflash, secure digital, PC cards, and MMC memory cards markets. Article transferred from network:

Rom and RAM are both semiconductor memory, Rom is short for read only memory, and Ram is short for random access memory. ROM can still maintain data when the system stops power supply, while Ram usually loses data after power loss. A typical Ram is the computer memory.


Ram has two categories: static RAM (static RAM/SRAM). The speed of SRAM is very fast. It is the fastest storage device for reading and writing, but it is also very expensive, therefore, it can only be used in demanding scenarios, such as CPU Level 1 buffering and level 2 buffering. The other is dynamic RAM (Dynamic RAM/Dram). DRAM retains data for a short period of time and is slower than SRAM, but it is faster than any Rom, but in terms of price, DRAM is much cheaper than SRAM, and computer memory is dram.


DRAM is divided into many types. Common types include fpram/fastpage, edoram, SDRAM, ddr ram, RDRAM, sgram, and wram. Here we will introduce a ddr ram.


Ddr ram (date-rate RAM) is also called ddr sdram. The improved Ram is basically the same as that of SDRAM. The difference is that it can read and write data twice at a clock, this doubles the data transmission speed. This is the most widely used memory in computers, and it has a cost advantage. In fact, it beat Intel's other memory standard-Rambus DRAM. In many high-end graphics cards, high-speed ddr ram is also provided to increase the bandwidth, which can greatly improve the pixel rendering capability of the 3D accelerator card.


Memory Working principle:


Memory is used to store the data and programs currently in use (that is, execution). The memory of the computer we usually refer to dynamic memory (that is, Dram ), in dynamic memory, the so-called "dynamic" means that after we write data into dram, data will be lost after a period of time, so we need a memory refresh operation by using a peripheral circuit.


The specific working process is as follows: whether a dram storage unit stores 0 or 1 depends on whether the capacitor has a charge. If there is a charge, it indicates 1, and if there is no charge, it indicates 0. However, after a long period of time, the capacitance of 1 will be discharged, indicating that the capacitance of 0 will absorb the charge, which is the cause of data loss. The refresh operation regularly checks the capacitance, if the power is greater than 1/2 of the full power, it indicates 1 and the capacitor is fully charged. If the power is less than 1/2, it indicates 0 and the capacitor is discharged, to maintain data continuity.


There are also many types of Rom. The difference between the prom and the EPROM is that the prom is one-time, that is, after the software is filled in, it cannot be modified. This is an early product and cannot be used now. The EPROM is used to erase the original program through ultraviolet radiation and is a general memory. Another type of EEPROM is an electronic interface. It has a high price, a long write time, and a low write speed.


For example, the mobile phone software is usually placed in the EEPROM. When we call, some of the last dialing numbers are temporarily stored in the SRAM, rather than writing the pass record immediately (the call record is stored in the EEPROM ), at that time, there was a lot of important work (CALLS) to do. If you write data, a long wait would be unbearable for users.


Flash Memory, also known as flash memory, combines the strengths of ROM and Ram, not only has the electronic Erasable Programmable (EEPROM) performance, data will not be lost after power failure, and data can be quickly read (NVRAM advantage), which is used in USB flash drives and MP3. In the past 20 years, embedded systems have been using ROM (EPROM) as their storage devices. However, in recent years, Flash has completely replaced the position of RoM (EPROM) in embedded systems, it is used to store bootloader, operating system or program code, or directly used as a hard disk (USB flash disk ).


Currently, there are two types of FLASH: nor flash and nadn flash.


The reading of nor flash is the same as that of our common SDRAM. Users can directly run the code loaded in nor flash, which can reduce the capacity of SRAM and save costs.


NAND Flash does not adopt the random read Technology of memory. It reads a block at a time, usually 512 bytes at a time. Flash with this technology is cheaper. Users cannot directly run the code on NAND Flash. Therefore, many development boards that use NAND Flash use a small nor flash to run the startup code in addition to NAND flah.


Nor flash is usually used for small capacity. Because of its fast reading speed, it is used to store important information such as the operating system, while NAND Flash is used for large capacity, the most common nand flash application is the DOC (Disk On Chip) used in the embedded system and the "flash disk" we usually use, which can be erased online. Flash on the market is mainly from Intel, AMD, Fujitsu and toshba, while the main manufacturers of NAND Flash are Samsung and toshba.


Comparison between NAND Flash and nor flash


Nor and NAND are two major non-loss flash technologies on the market. Intel first developed nor Flash technology in 1988, which completely changed the previous situation where EPROM and EEPROM were integrated. Next, in 1989, Toshiba published the NAND Flash structure, emphasizing reducing the cost per bit and higher performance, and easily upgrading it through interfaces like disks. However, after more than a decade, a considerable number of hardware engineers are still confused about nor and NAND Flash.


Phase "Flash Memory" is often used with phase "nor memory. Many insiders do not know the advantages of NAND Flash compared with nor, because in most cases, Flash is only used to store a small amount of code, so nor flash is more suitable for some. Nand is an ideal solution for high data storage density.


Nor is the primary non-easy-to-lose Flash technology on the market. Nor is generally used to store a small amount of code. Nor is mainly used in the code storage media. Nor is characterized by simple application, no special interface circuit, and high transmission efficiency. It is an internal chip execution (xip, execute in place ), in this way, the application can run directly in the (NOR) flash memory without having to read the code into the system Ram. In 1 ~ The small size of 4 MB has high cost efficiency, but the low write and erase speeds greatly affect its performance. Nor Flash has an SRAM interface and enough address pins to address it, so it can easily access every byte in it. Nor flash occupies 1 ~ Most of the 16 MB flash memory market.


The NAND structure provides a very high unit density, achieves a high storage density, and writes and erases quickly. The difficulty of using NAND lies in Flash management and special system interfaces.


1. Performance Comparison:


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 1 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.


(Note: The erasure time of nor flash sector varies depending on the brand and size. For example, for 4 M Flash, some sector erasure times are 60 ms, while some require a maximum of 6 s .)


2. Interface differences:


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.


3. Capacity and cost:


The unit size of NAND Flash is almost half the size of the nor device. Because the production process is simpler, the NAND structure can provide a higher capacity within the given mold size, thus reducing the price accordingly.


Nor flash occupies 1 ~ Most of the 16 MB flash memory market, while NAND Flash is only used in 8 ~ Among the MB products, this also shows that nor is mainly used in code storage media. NAND is suitable for data storage. NAND shares the largest share in the compactflash, secure digital, PC cards, and MMC memory cards markets.

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