Essentials of Computer Organization and Architecture, 5th Edition

3.3   LOGIC GATES

The logical operators AND, OR, and NOT that we have discussed have been represented thus far in an abstract sense using truth tables and Boolean expressions. The actual physical components, or digital circuits, such as those that perform arithmetic operations or make choices in a computer, are constructed from a number of primitive elements called gates. Gates implement each of the basic logic functions we have discussed. These gates are the basic building blocks for digital design. Formally, a gate is a small, electronic device that computes various functions of two-valued signals. More simply stated, a gate implements a simple Boolean function. To physically implement each gate requires from one to six or more transistors ...