Not to open a huge can of worms.... but... I always considered a mainframe to basically be a "fully decked out" minicomputer.
A minicomputer has a core CPU and memory (or racks of memory), then is "decked out" with data storage (racks of wall-sized tape decks), printers, pick-your-typewriter input (or two, or three), and maybe cabinets for serial IO or modem of some sort. So, sometimes I say mainframe when I really mean minicomputer (generally because mainframe just sounds cooler than "mini-computer" -- that is, mainframe clearly conveys the notion of "some big ass computer" whereas minicomputer just needs more clarification). What do you guys think? Or is a mainframe one of those giants so large, you walk inside its CPU? Or, is it like this... computer (a whole building, generally at least two story to support ac ducting and raised floor maintenance -- are these exclusively mainframes?) minicomputer (a single floor or room of a building or possibly a full top of a desk - and, these are NOT mainframes?) microcomputer (half a deck top or smaller, memory and accessories mostly self contained - doesn't necessarily have to have a microprocessor, but typically does) nanocomputer (modern MCU ? like Raspbery Pi) Also - on "personal computer", it's generally implied "digital electronic computers" so we don't have to dwell too much on rocks and beads as computers. Glad we didn't call them "coordinated electron pumpers" :) -Steve