Boolean logic


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Related to Boolean logic: Boolean search, Boolean expression, Boolean operators

Boolean logic

(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.



Curious About the Chip?


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 ?
Let a,b,a' and b' be the inputs to QCA circuit, c1,c2 and c3 are control inputs and y be the output, from table 2 we prove single circuit used to compute all Boolean logic functions.
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Boole, a teacher, was the widow of George Boole who gave his name to Boolean logic, but was also a gifted mathematician in her own right.
She gives practical advice on choosing sources and decoding database searches using keywords and Boolean logic, evaluating sources for reliability and fitness to the topic, locating relevant books and periodicals as well as other time-tested sources such as atlases and bibliographies, selecting academic electronic resources, getting the most of what can be a remarkably coy world wide web, and preparing citations.
With careful application of Boolean logic and a handful of clever hacks, experts could get there faster.
The system uses Boolean logic programming and a digital signal processor to perform reliably and quickly.
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.
For example, someone who earnestly believes that every college student needs a good dose of boolean logic whether they want it or not does not always advance the cause of the fifty-minute experience.
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He begins by imparting Boolean logic through a demonstration of a machine that plays tic-tac-toe.
use of Boolean logic ("and," "or" and "not" connectors), wildcards, etc.
Also, searches may be defined with complete Boolean logic and search results are displayed in a tree format to simplify the navigation to a classification.