Nor flash and nand flash are not clear, nornand

Nor flash and nand flash are not clear, nornand
Differences between nor flash and nand flash

I have been studying embedded systems for a while. I was confused when I first came into contact with nor and nand. I had to write a blog to remember clearly.

First, they are all storage devices, collectively referred to as flash memory. The reason for their difference must be the hardware difference. // It seems that men and women have different hardware before developing physiological differences

Different underlying causes of performance and usage (hardware): the logical device that makes up the storage unit. nor and non-gate, and nand adopt or non-gate. In fact, the so-called nor and nand are based on different manufacturing technologies. Literally, the nor is the non-gate, and the nand is the or non-gate, which is the smallest logical unit when the IC is made. It is like we say that the cmos device is built by a pmos and a nmos cmos as the basic unit.

Performance differences between nor and nand:

Differences between nor and nand interfaces:

Differences between nor and nand usage:

Q: What is the difference 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.
Flash memory can often be used with 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 features In-chip execution (XIP, eXecute In Place), so that applications can run directly In flash memory without having to read the code into system RAM. NOR transmission efficiency is very high, in 1 ~ The small size of 4 MB has high cost efficiency, but the low write and erase speeds greatly affect its performance.
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.

Performance Comparison
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.

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.

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.

Availability and Durability
When using the flahs media, it is possible to focus on the problem. Flash is a suitable storage solution for systems that need to expand MTBF. From the lifetime (durability), bit switching... the remaining full text>

The embedded system must have nand Flash and nor Flash?

To start a program, you must have a bootloader which must be stored in a non-power-down memory. Therefore, there must be at least one kind of bootloader in the system, which is usually either nor, or nand, or kernel or file system, environment Variables