Flash memory really depends on which exact IC you are using, and how the firmware engineers coded the other parts of the system to work with the chip(s). NAND chips and NOR chips are constructed differently, and even two chips of the same part number made by the same manufacturer on the same day can have drastically different P/E counts. Most manufacturers provide a minimum rating for the number of Program/Erase cycles the chip is guaranteed for. Most IC’s are rated for over 100,000 P/E cycles, and can often exceed that; sometimes even lasting over one million cycles.
A deletion operation is when a block of memory on the chip is overwritten to its default state. Some circuits use a 1 as the default state, others use 0 as the default state. It really depends on how the firmware and hardware engineers design it. Almost activity that makes use of the flash is a full P/E cycle, with the exception of simply reading the value. The best way to think of a flash chip is as an SSD. In fact, all an SSD is in most cases is just a collection of NAND chips linked together and configured to run as a single piece of memeory.
Each flash chip has small sectors in it which can only be written to an entire sector at a time. In order to add something to or remove something from ROM, the entire sector has to be copied and rebuilt. This is why a 1 TB SSD only has ~980 GB of storage; it has to save room for when it has to rewrite a sector. This can be seen in the TI Calculator in that each app takes up a certain number of “pages” where each page is the same size. I forget where on this wiki it is mentioned, but I know it says somewhere that if you fill a whole page, and go even one byte onto a second page in the memory, the entirety of the two pages will be used and cannot be used for anything else; even though there is only one byte on the second page.
When a chip wears out, it will typically fail one or two sectors at a time. This can result in an app stopping to work or slow speeds in the best case, or can cause problems with the OS in the worst case. However, if a chip fails, your best bet is to just get a whole new device. It is possible to replace the IC, but you have to have the proper tools and training to do it. Even if you replace the chip, you will have lost all the data on it. To get the data back you would have to have a ROM Image and the tools to program the IC without using the OS
Knowing how many P/E cycles have been performed is usually impossible, since most firmware engineers don’t track it and the OS has no way to know how many sectors are having P/E cycles on them at any given moment. If you’re skilled enough to be able to connect directly to the ROM controller and are somehow lucky enough that the firmware engineer had a counter on for some particular sector, you might be able to get a rough estimate. But again, unless you deal with these systems daily, its practically impossible.
(account deleted) 29 Sep 2019 01:57
