How PCI Works

One cannot imagine working without computers, as we end up doing a number of things with their help.  Many types of communication like text, audio and video are  made using computers. The industry of computers is progressing day by day and new devices and components are being introduced. These devices are compatible with computers because of the buses (data transport systems) which transport the data from a component or device to CPU and vice versa. There are two main types of buses

System Bus

It is used to transport data between system memory and CPU and transport the data at much faster speed than any other Bus including PCI.


PCI bus is comparatively slower than system bus and it is used for connecting hardware devices like modems, sound devices, graphic devices and hard disks to the computer. It is connected to CPU via Bus Bridge which connects PCI devices and ISA devices to the CPU.

PCI refers to Peripheral Component Interconnect. The work on PCI started in 1990 at Intel’s Architecture Development Lab. PCI were not put into every computer just after they were introduced but it took more than 4 years to make a significant mark and replace other buses like ISA and VESA Local Bus. The fact was that Microsoft introduced Windows 95 which supported a new feature called Plug and Play (PnP) and this boosted up the demand of PCI by great value. PnP is basically a core utility of BIOS. A PCI-based hardware is just inserted and the PnP feature itself recognizes the hardware, installs it and makes it ready to use.

There are some other buses like universal serial bus(USB) which are quite different from these two in function, as they connect devices like phones, cameras, printers and scanners with the computer.

How PCI works

PCI works in a very simple yet managed manner to transport the data to CPU. PCI devices are connected to the PCI bus which is connected to the Bus Bridge which is further connected to the CPU. It is connected in the following manner:

PCI device   > PCI bus   > Bus Bridge   > System Bus   > CPU.

This is the way a PCI device or hardware is connected to the CPU. ISA devices can also be connected to the CPU via Bus Bridge which is further connected to the PCI bus and so on.

PCI devices are very simple to install because of the Plug and Play feature. You just have to insert a PCI-based hardware in any of the empty PCI slot and the CPU will itself detect and install the driver.


Some specifications of PCI are:

  • PCI cards usually have 47 pins (except mastering cards which have 49 pins)
  • PCI is based on the Plug and Play feature which makes adding hardware easy.
  • PCI cards are operated at two voltages: 3.3 volts and 5 volts.
  • PCI cards are of two bandwidths: 32-bit and 64-bit.
  • PCI bus speed ranges from 33MHz to 133MHz.
  • PCI data transfer speed is from 132 Mbps to 1 Gbps.

Future of PCI

A lot of people think that PCI bus cannot be replaced but some computer experts have the opinion that as PCI replaced ISA, some new bus system will also replace it in near future. They say that PCI has approximately reached the upper limit of its capacity and would soon be replaced by any other Bus system.

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