What is an internal mask ROM?

Question

Microcontrollers

ROM stores the instruction address of the executable program

Answer 1

ROM - read-only memory (ROM - Read-Only Memory). A device (often in the form of a microchip) capable of storing some data for a long time without a power source. There are rewritable (flash drive, as a kind of EEPROM, for example) and non-rewritable.
Mask ROM - one of the varieties of ROM by the manufacturing method, not rewritable.
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Answer 2

https://ru.bmstu.wiki/ROM_(Read-only_memory)#ROM