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3

Early 8" floppy drives using mains-powered induction motors were speed-locked to the 50/60Hz mains frequency which determined (in most cases including a reduction gearing using a belt drive) the rotational speed of the floppy disk. This used to be the easiest and most exact way to maintain constant RPMs but also manifested itself in the disk format ...


3

Z-RAM installs into the CPU and MMU sockets of the IIc (the chips have to be removed from the motherboard and placed on the Z-RAM). The memory expansion connector that later IIcs have is not used. Even if there aren't any physical "slots" in the IIc, its operating system uses "virtual slots" for compatibility with the classic Apple II. (...


4

Almost certainly the Royal Navy's Comprehensive Display System. Although it did not have controls around the entire display, and the controls were generally momentary toggle switches, not buttons, it's basically what you're looking for. This was one of those inventions that no one hears about because of the particular way the British kept everything secret ...


5

All the Apple //c machines from September 1986 onward have an additional 34-pin header on the motherboard designed for memory expansion boards. Apple offered their own expansion board which support up to 1MiB of additional memory internal to the Apple //c. Other manufacturers, such as Applied Engineering offered 3rd party versions of these memory expansion ...


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