To achieve more than 100.000 cycles of writing and reading a 16 bit word to a serial EEPROM I once, a while ago, wrote something like this (not actual code):

unsigned int FetchEE (void)
{
unsigned int offset;
unsigned int data ;
  while (!offset)
  {
    for (offset = 0 ; offset < EEsize; offset++)
    {
      data = ReadIntFromEE(offset) // execute BIOS routine
      if ( data  != 0xffff) break ;
    }
  }
  offset--;
  data = ReadIntFromEE(offset);
  return (data); 
}


void WriteEE (unsigned int data)
{
unsigned int offset;
bit flag = FALSE;
 ;
  while (!flag)
  {
    for (offset = 0 ; offset < EEsize; offset++)
    {
      data = ReadIntFromEE(offset) // execute BIOS routine
      if ( data  = 0xffff)
      {
        flag = TRUE;
        break ;
      } 
    }
    if (!flag)
    {
      EraseEE();
      flag = FALSE;
    }
  }
  data = WriteIntToEE(offset);
  return (data); 
}

While this works quite well, I am now going to use a larger serial EEPROM for another project and this will take a very long time when at the end.
Does anyone have a better idea?

Erik