The Mac LC II (a.k.a. Performa 400, 405, 410, and 430) has 4 MB of RAM soldered to the motherboard and room for two additional SIMMs. (Apple says that some LC IIs have 2 MB of onboard RAM, but I have never run into one.)
What was the smallest desktop Mac prior to the Mac mini? Apple’s LC series, which measured just under 3″ tall, although it had as big a footprint as four minis.