Introduction to Computer System                                                                                                              Print this page
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Two instructions are fetch simultaneously from M and transferred to the program control unit. The instruction that is not to be executed immediately is placed in the instruction buffer register IBR. The opcode of the other instruction is placed in the instruction register IR where it is decoded.

In the decoding phase, the control circuits generate the required control signals to perform the specified operation in the instruction.

The program counter(PC) is used to store the address of the next instruction to be fetched from memory.

Input Output Device :

Input devies are used to put the information into computer. With the help of input devices we can store information in memory so that CPU can use it. Program or data is read into main memory from input device or secondary storage under the control of CPU input instruction.

Output devices are used to output the information from computer. If some results are evaluated by computer and it is stored in computer, then with the help of output devices, we can present it to the user. Output data from the main memory go to output device under the control of CPU output instruction.

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