I have a couple of IKEA-like boxes in my home office labeled “Inbox”. They are full of stuff I buy and store waiting for some free time to spend on them. From time to time I pick one of the boxes and take a look at its contents. They are actually full of “wow” stuff. I would buy again most of the things there but at the same time I fear I’m just collecting stuff that will become junk.
I couple of week ago I rescued from one of those boxes an M5Stack Core Development Kit and some other stuff that was there for maybe 6 months.
The Arduino Core for ESP8266 and ESP32 uses one SPI flash memory sector to emulate an EEPROM. When you initialize the EEPROM object (calling begin) it reads the contents of the sector into a memory buffer. Reading a writing is done over that in-memory buffer. Whenever you call commit it write the contents back to the flash sector.
Due to the nature of this flash memory (NOR) a full sector erase must be done prior to write any new data. If a power failure (intended or not) happens during this process the sector data is lost.
Also, writing data to a NOR memory can be done byte by byte but only to change a 1 to a 0. The only way to turn 0s to 1s is to perform a sector erase which turns all memory positions in that sector to 1. But sector erasing must be done in full sectors, thus wearing out the flash memory faster.