![]() ![]() The ALU is capable of applying a range of Boolean logic combinations to its input data (operands). ![]() You might think of his as dynamic configuration of the ALUs capabilities. The CPU decodes the instructions to select the appropriate function of the ALU. The ALU is also used to test multi-bit values for zero or negative values, or compare two multi-bit values for equality, less than, greater than etc. ![]() The ALU can shift the multi-bit value left of right (usually through some internal bit) shift is important for multiply and divide operations, among other uses. The ALU implements bit-wise Boolean operations like and, or, not (bit-complement), using the multi-bit values as groups of bits. The ALU implements the 'data processing' operations like add, subtract, negate, etc., using the multi-bit values to represent binary numbers. ![]() The ALU operates on multi-bit binary values, for example 8-bit (bytes), 16 or 32 bit words. If you search the web for Arithmetic Logic Unit, or ALU, you will find many usable explanations, for example wikipedia Arithmetic_logic_unitĪll Central Processing Units (CPUs) have one or more ALU's. Reading your question, it doesn't seem tht the book has communicated the basic concept of an Arithmetic Logic Unit (aka ALU). I don't have the Charles Petzold 'Code' book. ![]()
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