The BBC Micro (originally known as the Acorn Proton until BBC took over to market it since it was chosen for their literacy programme) is a computer made by Acorn. Rather like the Apple II in the US, it was mostly used as an educational computer to learn how to program in schools and also because it was expensive to buy meaning very few home owners had access to the machine. It was famous however for Elite, one of the most advanced games of the early 1980s.
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MAME supports the BBC Micro and is well supported thanks to the work of Nigel Barnes who has preserved this system and the Acorn Electron.
BeebEm is an emulator that supports every model of the BBC Micro. One may not understand how to load tapes or disks at first because it requires a key command, and also you must load a "boot" and a "start" rom in disk 0 and disk 1 respectively in order to load your game.