NAND flash memory has a lifespan of about 100 Kbytes of write cycles per block. And each block is usually 128 KB or 256 KB. I don’t know what type of NAND flash memory for iPad is used, but with the 16 GB version, a perfect wear leveling algorithm, writing a block every 5 seconds means:
16 /128 = 131072
131072 * 5 = 655360 (7,6 )
655360 * 100K = 2078 .
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