I am finding a problem with M27C512.

If I read it multiple times from the same eprom (powering the controller 9 volt as required), the bin files are identical and up to here is fine.

If I read a first eprom M27C512 and save the file .bin (64 Kbite); write the file .bin on an eprom and re-read the file.....comparing the two files with a hex editor but they differ by only one bit

With a second eprom instead of the file .bin differ totally.

I do not understand why