几个很好的nand nor flash的网页

Ext2,ext3,XFS,JFS,FAT and other "conventional" file systems work with block devices. They are designed this way. Flashes are not block devices,they are very different beasts. Please,read?this,and?this?FAQ entries.

Please,do not be confused by USB stick,MMC,SD,CompactFlash and other popular removable devices. Although they are also called "flash",they are not MTD devices. They are out of MTD subsystem's scope. Please,read?this?FAQ entry.

In order to use one of conventional file systems over an MTD device,you need a software layer which emulates a block device over the MTD device. These layers are often calledFlash Translation Layers?(FTLs).

There is an?extremely?simple FTL layer in Linux MTD subsystem -?mtdblock. It emulates block devices over MTD devices. There is also an?mtdblock_ro?module which emulates read-only block devices. When you load this module,it creates a block device for each MTD device in the system. The block devices are then accessible via?/dev/mtdblockX?device nodes.

But in many cases using?mtdblock?is a very bad idea because what it basically does if you change any sector of your mtdblockX device,it reads the whole corresponding eraseblock into the memory,erases the eraseblock,changes the sector in RAM,and writes the whole eraseblock back. This is very straightforward. If you have a power failure when the eraseblock is being erased,you lose all the block device sectors in it. The flash will likely decay soon because you will wear few eraseblocks out - most probably those ones which contain FAT/bitmap/inode table/etc.

Unfortunately it is a rather difficult task to create a good FTL layer and nobody still managed to implement one for Linux. But now when we have UBI (see?here) it is much easier to do it on top of UBI.

It makes sense to use?mtdblock_ro?for read-only file systems or read-only mounts. For example,one may use SquashFS as it compresses data quite well. But think twice before using?mtdblock?in read-write mode. And don't try to use it on NAND flash as it is does not handle bad eraseblocks.

载自 ：http://www.linux-mtd.infradead.org/faq/general.html

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NAND vs. NOR

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 from there. It must be loaded into RAM memory and executed from there.