MCS-5 1 is the core of single chip microcomputer invented by INTEL, and later this core (patent) was sold to semiconductor companies all over the world, so MCS-5 1 single chip microcomputer blossomed everywhere. The aforementioned AT89C5 1 and at89c 5 1 belong to MCS-5 1 core, which is abbreviated as 5 1 core.
805 1 is the genuine MCS-5 1 of INTEL company, and there is an unchangeable program storage ROM called mask ROM (mask ROM is made into a single-chip microcomputer at the time of chip manufacturing, with low cost, but it needs to be mass-produced, and it is not EPROM, EEPROM or FLASH-ROM).