# Boolean logic

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(mathematics)

## Boolean logic

The "mathematics of logic," developed by English mathematician George Boole in the mid-19th century. Its rules govern logical functions (true/false) and are the foundation of all electronic circuits in the computer. As add, subtract, multiply and divide are the primary operations of arithmetic, AND, OR and NOT are the primary operations of Boolean logic. Boolean logic is turned into logic gates on the chip, and the logic gates make up logic circuits that perform functions such as how to add two numbers together.

Various permutations of AND, OR and NOT are used, including NAND, NOR, XOR and XNOR. The rules, or truth tables, for AND, OR and NOT follow. See Boolean search, binary, logic gate and Bebop to the Boolean Boogie.

An AND Gate (Wired in Series) AND requires both inputs to be present in order to provide output. When both inputs pulse both switches closed, current flows from the source to the output.

Wired in patterns of Boolean logic and in less space than a postage stamp, transistors in one of today's high-speed chips collectively open and close quadrillions of times every second. If you are curious about how it really works down deep in the layers of the silicon, read the rest of "Boolean logic," then "chip" and, finally, "transistor." It is a fascinating venture into a microscopic world.

The following AND, OR and NOT examples use mechanical switches to show open and closed transistors. The switching part of an actual transistor is solid state (see transistor).

An AND Gate (Wired in Series) AND requires both inputs to be present in order to provide output. When both inputs pulse both switches closed, current flows from the source to the output.

An OR Gate (Wired in Parallel) OR requires only one of the two inputs to be present in order for current to flow from the source to the output.

A NOT Gate (Input Is Reversed) No pulse in puts current out (as shown). A pulse in puts no current out, as follows: an input pulse closes switch #1 and the current goes to #2. Switch #2 is normally closed, and a pulse from #1 opens it and stops the flow.

The Hierarchy The gates make up circuits, and circuits make up logical devices, such as a CPU. We're going to look at a circuit that is present in every computer. It adds one bit to another.

Adding Two Bits Together The half-adder circuit adds one bit to another and yields a one-bit result with one carry bit. This circuit in combination with a shift register, which moves over to the next bit, is how a string of binary numbers are added. This diagram shows the four possible binary additions for two bits.

The Half-Adder Circuit Trace the current through the example above. See how AND, OR and NOT react to their inputs. The 1 is represented in red (flow of current), and the 0 in blue (no current). Try it yourself below.

Try It Yourself Print this diagram and try your Boolean skill. Review the combinations of 0 and 1 above and pick any pair. With a pen or pencil, draw a line to represent a 1. Draw nothing for 0, and see if you can get the right answer.

Try It Yourself Print this diagram and try your Boolean skill. Review the combinations of 0 and 1 above and pick any pair. With a pen or pencil, draw a line to represent a 1. Draw nothing for 0, and see if you can get the right answer.
References in periodicals archive ?
The Option nodes basically represent the OR boolean logic operations.
i) Human judgments, such as attitude judgments, are often not simply read out from memory, but rather, they are constructed from the cognitive state for the question at hand; and (ii) drawing a conclusion from one question changes the context and disturbs the cognitive system, which then (iii) affects the answer to the next question, producing order effects, so that (iv) human judgments do not always obey the commutative rule of Boolean logic.
Simply put, Boolean logic is the algebraic interpretation of truth tables.
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Capable of many sophisticated sequences of operations, the system's field configuration program is based on Boolean logic statements.
One of the most commonly used search principles is Boolean logic, which refers to the logical relationship among search terms.
Mechanics of searching, including Boolean logic and truncation.
Even in doctoral seminars that I teach, I find the need to explain Boolean logic and patiently teach students how to develop search strategies, formulate queries, and even how to compute the precision of searches.
Without having to learn Boolean logic or wrestle with if-then-else logic, Dewqs' NMS makes it easy to rid your inbox of unwanted emails.
Boolean logic can be used to search by keyword, date, format, language, title, author, subject, or any combination of these.

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