The OMAP3 in the Pandora has an estimated 20 year life when operating entirely under recommended specification. That's 100% CPU usage over 20 years of course, but still very finite.
That's what the manufacturer specifies. This does not necessarily have to be the same as the real lifespan. I have yet to see a CPU that has failed due to normal wear out. Sure, it is possible that TI manufactures such chips without any saftey margin, but I guess their 20 years claim is rather something they can safely assume, not so much a real limit.
Something like 3 years, writing half the capacity every day?
Yes, that's a much more useful number.
Would that then be 6 years writing quarter the capacity I wonder?
Yes, it should work that way. But keep in mind, those numbers are specified for writing from beginning to end. No random access writes. This matters because if you randomly write data to the chip, actually much more data will be written to the flash memory, because of the flash's typically fairly large erase block size.
And 30 years writing 10% the capacity every day?
Probably not. For flash memory usually not only the amount of total data writes is specified, but also the time which the memory is guaranteed to retain its contents, which is usually in the order of 10 years. Older flash memory usually lasts longer than more modern memory. The smaller the process the memory is produced in, the smaller the amount of data that can be written as well as the amount of time the data is guaranteed to be readable.
Average writing 1.6GB every day for 30 years before it fails does seem like a lot, I dunno. It still doesn't explain what a failure is, or it probably does in that document somewhere and I just didn't read it properly, I'll have another look later.
1.6 GB of write to internal flash of a device like the Pyra seems like a lot indeed, but as those writes are typically rather random, the actual amout of data written can be a lot less, than what is written to the flash internally. Let's say you write lots of files with 4 kB of size each and they are randomly distributed over the disk, it could happen that for each of those files you have to first read 512 kB and then rewrite those 512 kB back to disk, assuming the erase block size is 512 kB (which is a typical value, could be even larger). In that case the actual amount of data would be more than 100 times of what you intended to write to disk. Both the flash controller as well as the OS try to prevent that, but it cannot be prevented entirely.
And how does that actually relate to the MTBF that was given before? Is that actually 239 years writing half the capacity every day? Or some other metric?
The metric for MTBF is usually pretty arbitrary and (obviously) a very theoretical value. MTBF is used in lots of scenarios, for example it is also used for harddisks. In that case the MTBF specifies the theoretical amount of time between two read errors (which can not be hidden from the OS by the harddisk's electronic). The MTBF numbers in hours for harddisks are often something like 1000000 hours, which most of you guys probably would agree, is not what one can expect as the harddisk's lifetime.
For record, how do you think flash memory "dies"? Because from your arguments it sounds like you're worried about the whole thing just one day failing but I'm pretty sure you don't think that.
No, it doesn't die that way. What usually happens is that at some point flash memory cells begin to fail. Depending on whether the flash memory has some internal memory reserved or not, you would see those errors sooner or later. What then happens is that you can no longer write to those damaged cells, but you can usually still read them. The flash controller tries to hide that from you as long as possible, but will eventually fail to do so. So the usable capacity shrinks over time. At some point all the memory will be read-only (in the best case) or no longer accessible at all (in the worst case). I've seen both.
