For by them I perceived it to be possible to arrive at knowledge highly useful in life; and in room of the Speculative Philosophy usually taught in the Schools, to discover a Practical, by means of which, knowing the force and action of fire, water, air, the stars, the heavens, and all the other bodies that surround us, as distinctly as we know the various crafts of our artizans, we might also apply them in the same way to all the uses to which they are adapted, and thus render ourselves the lords and possessors of nature.

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Reverse-engineering the 8085’s ALU and its hidden registers (righto.com) This article describes how the ALU of the 8085 microprocessor works and how it interacts with the rest of the chip, based on reverse-engineering of the silicon. (This is part 2 of my ALU reverse-engineering; part 1 described the circuit for a single ALU bit.) Along with the accumulator, the ALU uses two undocumented registers - ACT and TMP - and this article describes how they work in detail, as well as how the ALU is controlled.