It’s hard to remember what memory expansion options were like the further back we go, but peeking through the mags of the eighties has really opened my eyes on what enthusiasts had worked with back then like this memory cartridge from Mosaic Electronics in this ad from 1982.
This one seemed to be for the Atari 800 which initially came with a beefy 8 KB of memory. With this cartridge, it could be expanded with a whopping 32 KB. A handy chart showed the configurations you could use it in with a few marked “Danger! This Configuration Can Damage Computer.” All this for the low, low price of $179.95 at your nearest Mosaic retailer.