Control Bus

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What Does Control Bus Mean?

A control bus is a computer bus that is used by the CPU to communicate with devices that are contained within the computer. This occurs through physical connections such as cables or printed circuits.


The CPU transmits a variety of control signals to components and devices to transmit control signals to the CPU using the control bus. One of the main objectives of a bus is to minimize the lines that are needed for communication. An individual bus permits communication between devices using one data channel. The control bus is bidirectional and assists the CPU in synchronizing control signals to internal devices and external components. It is comprised of interrupt lines, byte enable lines, read/write signals and status lines.

Techopedia Explains Control Bus

Although a CPU can have its own distinctive set of control signals, some controls are common to all CPUs:

  • Interrupt Request (IRQ) Lines: Hardware line used by devices to interrupt signals to the CPU. It allows the CPU to interrupt its current job to process the present request.
  • System Clock Control Line: Delivers the internal timing for various devices on the motherboard and CPU.

The majority of system buses are made up of 50 to 100 distinct lines for communication. The system bus consists of three types of buses:

  • Data Bus: Carries the data that needs processing
  • Address Bus: Determines where data should be sent
  • Control Bus: Determines data processing

Communication between the CPU and control bus is necessary for running a proficient and functional system. Without the control bus the CPU cannot determine whether the system is receiving or sending data. It is the control bus that regulates which direction the write and read information need to go. The control bus contains a control line for write instructions and a control line for read instructions. When the CPU writes data to the main memory, it transmits a signal to the write command line. The CPU also sends a signal to the read command line when it needs to read. This signal permits the CPU to receive or transmit data from main memory.


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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.