A computer’s main memory is organized in manageable units called cells, with a typical cell size being eight bits (eight bits = one byte). Small computers used in such household devices as microwave ovens may have main memories consisting of only a few hundred cells, whereas large computers may have billions of cells in their main memories. Although there is no left or right within a computer, we normally envision he bits within a memory cell as being arranged in a row. The left end of this row is called the high-order end, and the right end is called the
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When considering the internal activities of a computer, we must deal with string of bits, some of which can be quite long. A long string of bits is often called a stream. Unfortunately, streams are difficult for the human mind to comprehend. Merely transcribing the pattern 101101010011 is tedious and prone error job. To simplify the representation of such bit patterns, therefore, we usually use a shorthand notation called hexadecimal notation, which takes advantage of the fact that bit patterns within a machine tend to have lengths in multiples of four. In particular, hexadecimal notation uses a single symbol to
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A device that produces the output of a Boolean operation when given the operation’s input values is called a gate. Gates can be constructed from a variety of technologies such as gears, relays, and optic devices. Inside today’s computers, gates are usually implemented as small electronic circuits in which the digits 0 and 1 are represented as voltage levels. We need not concern ourselves with such details, however. For our purposes, it suffices to represent gates in their symbolic form.
Boolean Operations AND, OR, XOR (exclusive or)
Note that the AND, OR, XOR, and NOT gates are represented by distinctively shaped
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