INTERNAL BUS OF COMPUTERS BASIC INFORMATION

Input/output ports are used to connect the computer to external devices. Input and output standards described in the previous sections are referred to as external bus standards.

In addition to these external buses, computers also have internal buses that carry address, data and control signals between the CPU, cache memory, SRAM, DRAM, disk drives, expansion slots and other internal devices. Internal buses are of three types, namely the local bus, the PCI bus and the ISA bus.

Local Bus

This bus connects the microprocessor to the cache memory, main memory, coprocessor and PCI bus controller. It includes the data bus, the address bus and the control bus.

It is also referred to as the primary bus. This bus has high throughput rates, which is not possible with buses using expansion slots.

PCI Bus

The peripheral control interconnect (PCI) bus is used for interfacing the microprocessor with external devices such as hard disks, sound cards, etc., via expansion slots. It has a VESA local bus as the standard expansion bus.

Variants of the PCI bus include PCI 2.2, PCI 2.3, PCI 3.0, PCI-X, PCI-X 2.0, Mini PCI, Cardbus, Compact PCI and PC/104-Plus. The PCI bus will be superseded by the PCI Express bus. PCI originally had 32 bits and operated at 33 MHz. Various variants have different bits and data transfer rates.

ISA Bus

The industry-standard architecture (ISA) bus is a computer standard bus for IBM-compatible computers. It is available in eight-bit and 16-bit versions.

The VESA local bus was designed to solve the bandwidth problem of the ISA bus. It worked alongside the ISA bus where it acted as a high-speed conduit for memory-mapped I/O and DMA, while the ISA bus handled interrupts and port-mapped I/O.

Both these buses have been replaced by the PCI bus.