How the CPU executes program instructions

How the CPU executes program instructions - Reading: *How...

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          Reading: *How the CPU executes program instructions * Let us examine the way the central processing unit, in association with memory, executes a computer program. Many personal computers can execute instructions in less than one millionth of s second, whereas supercomputers can execute instructions in less than one billionth of a second. Before an instruction can be executed, program instructions and data must be placed into memory from an input device or a secondary storage device. The data will probably make a temporary stop in a register. Once the necessary data and instruction are in memory, the central processing unit performs the following four steps for each instruction: 1. The control unit fetches (gets) the instruction from the memory. 2. The control unit decodes the instruction (decides what it means) and directs that the necessary data be moved to the Arithmetic/ Logic Unit (ALU). These first two steps together are called instruction time or T-time. 3. The ALU executes the arithmetic or logical instruction. That is, the ALU is given control and performs the actual operation on the data. 4. The ALU stores the results of this operation in memory or in a register. Steps 3 and 4 together are called execution time, or E-time. Figure 1: The machine cycle The control unit eventually directs memory to release the result to an output device or a secondary storage device. The combination of T-time and E-time is called the machine cycle. Comprehension check : Decide whether these statements are True or false. Justify your answer. Statements True False 1. Supercomputers execute instructions slower than personal computers. Justification: ……………………………………………………………………………………… …………. . ……………………………………………………………………………………… ………………………………. 2.
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How the CPU executes program instructions - Reading: *How...

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