Control Buses In PC

System bus is the PC’s main shipping system that hook ups its main components – CPU, Memory, Control logic and Input-Output (I/O Ports). Similar to its road-going name-sake, the bus is basically the means of turning over something – in this case digital information – from one place to another. The system bus can be view as three divergent parts: The address bus, the data bus and the control bus, which put into words address, data and control signals between the CPU, memory and other devices. The most common type of memory admittance is to transfer data to and from the CPU. The microprocessor obtains a byte of data from memory as follows. First, the address of the memory location required is placed on the address bus and a signal is then sent on the MEMR line of the control bus. This tells the hardware to copy the contents of that memory location onto the data bus so that it can read into one of the processors registers. A byte is written to memory in a similar way. The address is positioned on the address bus and the byte of data is placed on the data bus. A MEMW signal is send, and the hardware then stores the data value in the memory location specified, overwriting the previous contents. Each read or write is known as a memory cycle.