![]() ![]() ![]() Each carry from one column is added to the next column. An addition marches consistently from the rightmost column of digits to the leftmost column. Addition and subtraction complement each other in some ways, but the mechanics of the two operations are different. Chapter 13. But What About Subtraction? After you’ve convinced yourself that relays can indeed be wired together to add binary numbers, you might ask, “But what about subtraction?” Rest assured that you’re not making a nuisance of yourself by asking questions like this you’re actually being quite perceptive. Building an 8-Bit Adder still requires 144 transistors (more if you replace the ripple carry with a look-ahead carry), but the circuit is microscopic. When used in computers, transistors basically function the same way relays do, but (as we’ll see) they’re much faster and much smaller and much quieter and use much less power and are much cheaper. ![]()
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