EEPROM, a type of memory chip where you can store data, has limited number of writes. Usually most EEPROMs are rated at 100,000 writes.
Well, if you wanna find out how much writing you can actually do, you can build yourself a DIY EEPROM tester and just keep doing re-writes until the thing stops.
How long will it take to complete a million write-verify cycles? The Flash Destroyer’s current top speed is about 736 cycles per minute, or 22 hours to complete 1 million writes. Back that off to one write per second (11days) or per 10 seconds (110days) and the time increases dramatically. The Flash Destroyer has several alternative firmwares with different write speeds that can be loaded over USB.