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Dale - Computer Science Illuminated 149

Dale - Computer Science Illuminated 149 - to determine the...

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Arithmetic/logic unit The computer component that performs arithmetic operations (addition, subtraction, multiplica- tion, division) and logical operations (comparison of two values) 122 Chapter 5 Computing Components different memory addresses. Notice the relationship between the bits in the processor and the number of different addresses: n bits can address 2 n different locations. The cells in memory are numbered consecutively beginning with 0. For example, if the addressability is 8, and there are 256 cells of memory, the cells would be addressed as follows: What are the contents of address 11111110 ? The bit pattern stored at that location is 10101010. What does it mean? We can’t answer that question in the abstract. Does location 11111110 contain an instruction? A integer with a sign? A two’s complement value? Part of an image? Without knowing what the contents represent, we cannot determine what it means: It is just a bit pattern. We must apply an interpretation on any bit pattern
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Unformatted text preview: to determine the information it represents. When referring to the bits in a byte or word, the bits are numbered from right to left beginning with zero. The bits in address 11111110 above are numbered as follows: Arithmetic/Logic Unit The arithmetic/logic unit ( ALU ) is capable of performing basic arithmetic operations such as adding, subtracting, multiplying, and dividing two numbers. This unit is also capable of performing logical operations such as AND, OR, and NOT. The ALU operates on words; thus the word length of a computer is the size of the quantities processed by the ALU. The word length of the Pentium IV is 32 bits or 4 bytes. 1 – 2 1 6 – 7 1 8 – . 1 1 – – Bit position Contents Address –––––––– –––––––1 111111–– 111111–1 1111111– 11111111 ) ) ) Contents 111–––11 1–1–1––1 –––––––– 11111111 1–1–1–1– ––11––11 ) ) )...
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