How is an original arcace game converted to MAME?

I'm wondering how an original arcade cabinet is converted into a MAME rom. Do you have to take out the circuit board and plug it into a computer and move everything over to the computer? Or do programmers know how to recreate these games? Or is there some other method? I've searched and searched everywhere like crazy and I can't find anything about this.

the roms (data) are dumped, then the mame emulator has drivers for each (system)

 Dumped from where? The original arcade circuit board?

 the original circuit board

 Ah, I see now. Thank you for clearing that up.

there are devices called "ROM readers", where you plug the ROM chips from the arcade board and transfer their contents to a PC.

Mame emulates the arcade machines and runs the code from the dumped chips.

But the quarters! How do I get the quarters into my cwom-pewter?