If it’s physically impossible to write to a ROM (read-only memory) cartridge, how do manufacturers do it?

Question

Is somehow locked physically during production, or through software?

In: 210

Answer 1

Imagine a memory chip is like a chalkboard.

A read-and-write chip is a blank board. You can write on it with chalk as you want and erase and add as you please.

A read-only chip is akin to the board manufacturer carving words into the board when its made. These are now permanent and cant be altered by you. Theres no space for you to write with chalk, all of it is made of pre-carved information.

This was typically done in the factory by etching this data with a process called lithography onto the chip instead of having writable memory cells. Over time many different ways of making irreversible (or nearly so) data sets have been developed.