nor flash 与 nand flash 的区别

Beside the different silicon cell design, the most important difference between NAND and NOR Flash is the bus interface. NOR Flash is connected to a address / data bus direct like other memory devices as SRAM etc. NAND Flash uses a multiplexed I/O Interface with some additional control pins. NAND flash is a sequential access device appropriate for mass storage applications, while NOR flash is a random access device appropriate for code storage application.NOR Flash can be used for code storage and code execution. Code stored on NAND Flash can't be executed frome there. It must be loaded into RAM memory and executed from there.

                                           NOR                 NAND 
Interface                            Bus                   I/O 

Cell Size                             Large                Small 

Cell Cost                            High                   Low 

Read Time                          Fast                   Slow 

Program Time single Byte   Fast                  Slow 

Program Time multi Byte    Slow                    Fast 

Erase Time                         Slow                    Fast 

Power consumption            High              Low, but requires additional RAM 

 

Can execute code              Yes               No, but newer chips can execute a small loader out of the first page

Bit twiddling          nearly unrestricted    1-3 times, also known as "partial page program restriction"

Bad blocks at ship time         No                    Allowed

 

Some facts about write speed.
NAND is typically faster than NOR for large writes. A typical NOR write is 10uS per word, which results in 1280uS per 512 bytes on a 32-bit bus. A typical NAND write is 50nS per byte + 10uS page seek + 200uS program which results in 236uS per 512 bytes on a 8 bit bus.

As NAND Flash is cheaper than NOR Flash and has a very slim interface it was selected as the optimum solution for large nonvolatile storage applications such as solid state file storage, digital audio/voice recorder, digital still camera and portable applications requiring non-volatility.

 

以上内容转自：http://blog.csdn.net/hxliu_leo/archive/2010/03/09/5360097.aspx

在嵌入式系统中有 jffs和yaffs文件系统，jffs文件系统一般挂在nor flash上，而yaffs文件系统则针对nand flash做了专门的优化，所以一般挂在nand flash上。