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Kenbak-1

The Kenbak-1 (Kenbak Corporation, 1971) is widely credited as the first commercial personal computer. John Blankenbaker built it before the microprocessor existed, so there is no CPU chip: the processor is made entirely from TTL logic. It has 256 bytes of memory, three registers (A, B and X), and a front panel of eight lamps and buttons for programming it and reading it back. Here it runs real, originally-authored programs whose output lights the eight lamps, modelling the full instruction set and all five addressing modes. Open the debugger to single-step the TTL processor, disassemble memory, set breakpoints and write watchpoints, and inspect A / B / X / P and the overflow and carry flags. The Kenbak-1 has no audio hardware, so it is silent.