The difference between Nor and NAND Flash
1. Operating speed
When writing data and erasing a large amount of data, because NAND flash supports block operations, NAND is much faster than NOR, and the difference between the two is nearly a thousand times; but when the amount of data is small, such as a few bytes, Nor Flash is better than NAND. Flash erasing and writing speed is fast, because the read and write operations of NAND flash, although only a few bytes of operation, also need to rewrite the entire data block;
Since the NOR address line is separated from the data line, the NOR chip can be connected to the data line like SRAM. When reading data, NOR is faster than NAND. NOR is read in units of words or bytes. NAND must first send address information to the chip for addressing before reading data.
2. Comparison of capacity and cost
In the case of the same area and process, NAND FLASH capacity is much larger than NOR, the production cost is low, and it is easier to produce large-capacity chips, so it is relatively cheap to add one;
each memory cell of NOR type FLASH is connected to the bit line , Increasing the number of bit lines in the chip, which is not conducive to the improvement of storage density.
3. Ease of use
The I/O port of NAND FLASH uses multiplexed data lines and address lines, and data access must be performed serially through registers first. Different products or manufacturers have different signal definitions, which increases the difficulty of application. NandFlash devices use complex I/O ports to serially access data, and 8 pins are used to transmit control, address and data information, and the operation sequence is more complicated;
NOR FLASH has special address pins for addressing, making it easier to connect with other chips, and it also supports local execution. Application programs can run directly inside FLASH, which can simplify product design.
4. Durability
Generally, NAND erases and writes 1 million times, and NOR erases and writes 100,000 times. But the reliability of NOR is higher than that of NAND. This is mainly because the NOR-type interface is simple, less data operations, less bit swap operations, so it has high reliability, and there are few bad blocks, so it is generally used in high reliability requirements. The place. On the contrary, NAND-type interfaces and operations are relatively complex, and there are many bit swap operations. For critical data, error detection/error correction (EDC/ECC) algorithms are required to ensure data integrity, so the probability of problems is greater. In addition, bad blocks are inevitable, and because bad blocks are randomly distributed, even error correction cannot be done.
Nor and NAND Flash in common
The commonality of NAND and NOR chips is first manifested in that to write data to the chip, the corresponding content in the chip must be cleared first, and then written, which is commonly referred to as "erase first and write later." It's just that the NOR chip only needs to erase one word, while the NAND needs to erase the entire block. Secondly, the number of times the flash memory is erased and written is limited. When the use of the flash memory is close to its service life, write operations often fail; when the service life is reached, the data stored in the flash memory can be read, but cannot be written anymore. Therefore, in order to prevent the occurrence of the above problems, it is not possible to repeatedly write to a specific area. Generally, NAND can be erased and written more frequently than NOR chips, but because NAND is usually a block erase, if one of the pages in the block fails, the entire block will fail, and because the erase and write process is complex, the probability of failure is relatively high. , So on the whole, the life span of NOR is longer.
Another commonality is that the read and write operation of flash memory is not just a physical operation. In fact, data storage in flash memory must be implemented by algorithms. This module is generally in the MTD' (Memory Technology Drivers) module of the driver or in the FTLZ (Flash Translation) module. Layer) is implemented in the layer, and the specific algorithm is related to the chip manufacturer and chip model.