The article about the Tungsten T5 hat brought me quite a few comments-including a flame in German! Thanks to everybody who commented and helped me update my understanding of Flash chip architecture.
Actually, there are two types of flash: The NOR Flash and the NAND flash.
NOR Flash is the older of the two(developed by Intel 1988), and is the one I have practically used in my projects. Lets discuss the differences here:
This Flash memory type can be addressed byte for byte. It basically works like a SRAM chip that doesn’t loose data when powered off and works a bit slower. Flash’s are only sector-erasable.
Programs can be run from it because it basically is like RAM when being read-and it has been used ever since the Palm III to store the OS of the Handheld. It didn’t get lost when the Handheld was reset and out of power, but it could still be updated(I say could, because PalmOne didn’t always release Flash Upgrades recently, e.g. Tungsten T!). ROM’s couldn’t be updated….
This is the new kid on the block here-and I haven’t ever ever seen such a chip in action. You feed a sector address into the chip, and out comes a serial stream of the whole sector. Writing is also accomplished in whole sectors.
Since it is very difficult to execute a serial byte stream, programs cannot be directly run from this kind of flash! However, it is way cheaper than NOR flash.
This was an interesting stroll through electronics. I maybe get my lab back working someday(damn accident), then I will give you further coverage on the topic!
Find further Information in the Wikipedia on http://en.wikipedia.org/wiki/Flash_memory