The difference between nor flash and NAND type Flash

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(1) The basic unit of flash memory chip read and write different applications on nor chip operation with " word " as the basic unit. In order to facilitate the management of large or flash memory, nor flash memory is usually divided into 128KB or 64KB of logic blocks, and sometimes the block is also divided into sectors. Both logical block numbers and intra-block offsets need to be specified when reading and writing. Applications operate on NAND chips using "blocks" as the basic unit. NAND flash blocks are smaller, typically 8KB, and then each chunk is divided into pages, and the size of the page is typically 512 bytes. To modify a byte in the NAND chip, you must rewrite the entire data block.

(2) Nor flash memory is a random storage medium for the small amount of data , NAND flash memory is a continuous storage medium, suitable for large data storage.

(3) because the nor address line and the data line separate, so nor chip can be like SRAM connected to the data line. Nor chip is used similar to the usual memory chip, it is very efficient transmission, executable can be executed in the chip (XI P, execute in place), so that the application can run directly in Flash flash memory, no longer have to read the code into the system RAM. Because nor is this characteristic, the embedded system often uses nor chip to do the starting chip to use. NAND has a common address and data bus, need to connect some control input and output, so it is difficult to make the NAND chip start chip directly.

(4) NAND flash chip because of the common address and data bus for the reason, do not allow a byte or even a block to clean up, only a fixed size of the region to clear 0 operations, and nor chip can operate on the word. So the speed of handling small amounts of I/O operations is fast with NAND speed. For example, a nor chip usually write a word need 10 microseconds, then write 512 bytes on the 32-bit bus needs 1280 milliseconds, while the NAND flash write 512 bytes required time includes: 512x per byte 50 nanoseconds +10 microseconds of the page time spent on the patch of +200 microseconds =234 microseconds.

(5) NAND flash memory capacity is large, the current maximum capacity has reached 8G bytes. For ease of management, NAND storage space uses a block and page two storage system, that is, the storage space of flash memory is two-dimensional, such as the size of the K9F5608UOA flash block is 16K, the size of each page is 512 bytes, and 16 bytes per page of the idle area to hold the error check code space ( Sometimes referred to as out-of-band,oob space); During write operations, the NAND Flash puts a byte of data into the internal buffer each time, and then sends a "write instruction" for the write operation. Since the operation of the NAND flash is in blocks and pages, NAND is faster than nor flash when it reads and writes large amounts of data to NAND flash.

(6) Nor flash memory is more reliable than NAND flash, which is mainly due to the simple interface of nor type flash memory, less data operation, bit switching operation, so high reliability, very few bad blocks, and therefore generally used in high reliability requirements. Conversely, NAND flash interface and operation are relatively complex, bit switching operations are also many, critical data is the need for an error detection/error correction (EDC/ECC) algorithm to ensure the integrity of the data, so asked to prevent the above problem, can not be repeated to a specific area of the write operation. Usually NAND is more erasable than nor chip, but because the NAND is usually the whole piece of erase, the page within the block if there is a greater chance of a problem, bad block is inevitable, and because the bad block is randomly distributed, even error correction can not be done.

(7) NAND Flash general Address line and data line sharing, to read and write speed has a certain impact, and nor flash flash data cable and address line separate, so relatively fast reading and writing speed.

The common denominator of NAND and nor chips is that the first thing to write to the chip is to erase the corresponding contents of the chip before writing it, which is usually said to be "first wiped and then written." Only the NOR chip uses only one word to erase, and NAND needs to erase the entire block. Secondly The number of Flash Erase writes is limited. When the use of flash memory is close to the service life, the write operation will often fail, and when it reaches the service life, the data stored inside the flash memory can be read, but no further write operation will be invalidated, and due to the complex erase process, the probability of failure is relatively high, so the whole Longer life. Another common denominator is that the read and write operation of flash memory is not just a physical operation, but that the data stored on the flash memory must be implemented using the algorithm, which is typically in the driver's MTD ' (Memory technology Drivers) module or in Ftlz (flash Translation layer), the specific algorithm and chip manufacturers and chip models are related.

From a use point of view, nor flash and NAND flash are characteristic:

(1) nor has a low storage density, so the cost of storing one byte is higher, while the storage density and storage capacity of NAND flash memory are higher;

(2) NAND flash exists to erase, write files (especially continuous large files) very fast, very suitable for sequential reading occasions, and nor read fast, in the application of random access has good performance.

The difference between nor flash and NAND type Flash