Buses

• The address bus carried memory addresses that identify where data is being read from or written to
• The data bus carries the binary numbers that make up the actual information being transmitted around the CPU and computer
• The control bus carries command and control signals to and from every other component of the CPU and computer
• The control and data buses are bidirectional, meaning that they can be used to send data in both directions.
• The address bus is monodirectional, meaning that it only carries data in one direction (from the CPU to RAM)
• The control signals include:

  • Bus request: shows that a device is requesting the use of the data bus
  • Bus grant: shows that the CPU has granted access to the data bus
  • Memory write: data is written into the addressed location using this bus
  • Memory read: data is read from a specific location to be placed onto the data bus,
  • Interrupt request: shows that a device is requesting access to the CPU
  • Clock: used to synchronise operations
• Buses are a set of parallel wires which connect two or more components inside the CPU.
• Each wire on a bus transmits a single bit at any given time.
• The width of the bus is the number of parallel wires the bus has. The width of the bus is directly proportional to the number of bits that can be transferred simultaneously at any time.
• Buses are typically 8, 16, 32 or 64 wires wide.