The Atari 2600 could access 4K bytes natively. Bank selecting multiple (or larger) ROMs was known in the industry, although Atari was the first to do it in a game cartridge. At Activision I developed a pretty cool automatic bank switching system I called SCABS. https://twitter.com/GameResearch_E/status/1346513304542470144
SCABS (I know, disgusting acronym) stood for Subroutine Controlled Automatic Bank Switching. The game code could make subroutine calls between banks, and the circuit detected the operation and performed a bank switch between the JSR instruction and arrival at the destination.
All other bank switching systems require overhead processing that made them a pain to use. For example, every bank of the ROM has to have a small area of duplicate code to jump into, change banks, and jump out of so that the CPU is not executing code that switches with the bank.
SCABS could automatically access 8 banks of 4K, bringing the total memory from 4K to 32K bytes. We used this system briefly for (I think) Robot Tank and Decathlon. It required an external timing resistor on the PC board, so you can tell by looking at the board.
Adding a resistor cost a nickel (not to mention the extra circuitry in the ROM). Once Atari somehow got a patent on the use of bank switching in a game cartridge they offered it for a nickel per cartridge royalty. That made it cheaper for all of us and SCABS was abandoned.
You can follow @PitfallCreator.
Tip: mention @twtextapp on a Twitter thread with the keyword “unroll” to get a link to it.

Latest Threads Unrolled:

By continuing to use the site, you are consenting to the use of cookies as explained in our Cookie Policy to improve your experience.