Microprocessor Buses: Types, Functions, and Connections

Posted on Jan 7, 2025 in Computers

A microprocessor bus is a common set of power lines that connects all devices and computer components. Circuit loads are observed in these lines to identify the data and respond when your ID is transmitted. Then, they begin to transmit or receive data in another set of cables. This transport is the means by which data travel and may have the following characteristics:

  • Data Path Width: The number of bits that can be carried simultaneously.
  • Clock Cycle Speed: The number of data groups per second that can be sent by the data path. The elementary computer speed is usually called the front-side bus.
  • Bandwidth: The combination of the two, resulting in the number of bits per second that can travel through the bus.

Types of Buses

There are three main types of buses:

  • The data bus is bidirectional, as data can flow to or from the CPU.
  • The control bus is used to synchronize the activities and transactions with system peripherals.

Sorted by Way of Conveying Information

  • Unidirectional Bus: This type of bus is characterized by information flowing in only one direction.
  • Bidirectional Bus: Features that allow data to flow in either direction.
  • Serial Bus: Information can flow in one or two directions. The difference is that the information is transmitted bit by bit, so it can be considered slow compared to the parallel bus.
  • Parallel Bus: All information that is transmitted is sent through several channels simultaneously, making it faster than the serial bus.

Classified by Functionality

  • Microprocessor-Memory Buses: These are usually very fast, with a known number of devices and performance.
  • I/O Buses: These are open, slow, and wide, supporting an unknown number of devices with very mixed performances.
  • Backplane Bus: Microprocessor, memory devices, and I/O on the same bus.
  • Synchronous and Asynchronous Buses:
    • Synchronous Bus: Signals occur in a whole number of one clock cycle called a bus cycle, whose frequency is characteristic of the bus.
    • Asynchronous Bus: There is no master clock; the length of messages is characteristic of the device.

Types of Buses for Connecting Peripherals

EISA (Extended ISA)

This bus is, as its name indicates (Enhanced Industry Standard Architecture), an extension of the original ISA bus or AT.

VL-Bus (VESA Local Bus)

The homogenized VL-Bus is an expansion of the local bus, operating at 32 bits but capable of performing 16-bit operations.

PCI (Peripheral Component Interconnect)

Integrates control relating to all connected devices: DMA, interrupts, and data addressing.

SCSI (Small Computer System Interface)

It could be defined as an intelligent, accomplished, and bidirectional I/O subsystem. A single SCSI host adapter can control up to seven SCSI devices connected to it.

Advantages of SCSI:

  1. Removes any limitations that all PC BIOS may impose on the drives.
  2. Logical addressing eliminates the overhead that could be the host to maneuver the physical aspects of the device; the SCSI controller controls it.

SCSI can be configured in three different ways that give it great versatility:

  1. Single initiator/single target: The most common; the initiator is an adapter in a slot of a PC, and the target is the hard disk controller.
  2. Single initiator/multiple targets: Less common and rarely implemented, it is quite similar to the above, except that it controls different types of I/O devices (CD-ROM and hard drive).
  3. Multiple initiators/multiple targets: Much less used than the previous configurations, it fully exploits the capabilities of the bus.