Feature list: https://web.archive.org/web/20220926134250/https://support.a...
“The Centris 660AV and Quadra 840AV are the first Macintosh computers to implement a 2MB ROM using two 512Kx16 chips. The new ROM is also the first ROM that contains code for portions of System 7 that were able to be moved to the ROM, freeing up RAM for applications and other system use.”
Gary Davidian recollection: https://archive.computerhistory.org/resources/access/text/20...
“[F]or the Quadra 840AV they were starting [a universal ROM] over and with a newly built ROM from new sources and incorporating a lot of the stuff from System 7”
“It was called the Super Mario ROM. I don't know why it was called that but that was what it was called. So [AV Quadras] were the first Super Mario ROM product. And so yeah, I wanted— they had to ship and then, you know, System 7 was out before us and it forced us to bump RAM to 8 megabytes from 4.”