[spuggy]

Originally Posted by RWebb

thx - this means the silicon "wears" out from repeated writes?

at the junctions? or?

Actually, erase cycles. After enough of them, the block cannot be erased, one or more individual memory cells representing a single bit in a larger 8/16/32 bit quantity will get "stuck".

(Curiously, this is pretty much exactly the same way that old UV-erasable EEPROMs used as re-programmable replacements for the factory-supplied, write-once EPROM in the Motronics DME - usually a 2716 or 2732, IIRC - eventually fail in a regular programming rotation; they can no longer be erased/cleared. For these, not putting a sticker over the little quartz window and letting the UV in regular light randomly clear the charge from individual bits/cells over time - corrupting whatever data/program was stored there - is another)

The smallest block, with raw flash technology, that can be erased is quite large, somewhere between 64-128KiB - depending on the chip used and how it is organized internally.

Heh. It's been more than 10 years since I wanted to hack up a driver to manipulate Intel linear flash cards (as used on older Ciscos) directly in *BSD. Couldn't place my Intel spec documents.

So I cribbed the following from the excellent Linux MTD project Memory Technology Device (MTD) Subsystem for Linux.:

Eraseblocks wear-out and become bad and unusable after about 10^3 (for MLC NAND) - 10^5 (NOR, SLC NAND) erase cycles

The following table describes the differences between block devices and raw flashes. Note, SSD, MMC, eMMC, RS-MMC, SD, mini-SD, micro-SD, USB flash drive, CompactFlash, MemoryStick, MemoryStick Micro, and other FTL devices are block devices, not raw flash devices. Of course, hard drives are also block devices.

USB sticks, CompactFlash cards and other removable flash media are not MTD devices. They are block devices. They do contain flash chip inside, but they also contain some translation layer above which emulates block device. This translation layer is implemented in hardware. So for outside world these devices look exactly as hard drives, not like MTD devices.

and

Also note, these devices are "black boxes". The way they implement this flash-to-block device translation layer is not usually published. And in many cases the algorithms used at this layer are far from brilliant. For example, many USB sticks and other cards lose data in case of unclean reboots/power cuts. So, be very careful.