PCI stands for Peripheral Component Interconnect. This is a computer bus, utilized for the attachment of peripheral devices to the computer motherboard. Through PCI, a shared data path is implemented between the central processing unit and the marginal controllers found in all computer models that range from laptops to mainframes. PCI was first incorporated in computers in 1993 and developed by Intel Corporation. Soon it replaced the traditional ISA and VESA local bus to become the standard expansion bus used in today’s computers. The PCI device features are the play and plug devices, which load automatically when they are connected. The system firmware is tasked with the inspection of every device Peripheral Component Interconnect configuration space to distribute resources accordingly. Every device is allowed up to six areas of memory space or port space. Additional ROM provides the devices with EFI drivers and open firmware. When interruptions happen during the configuration of PCI, firmware allocates them to the device instead of jumpers on the card.
PCI bus connects the expansion drives and cards to the processor as well as other sub systems. The bus speed of the PCI bus on most systems is 33MHz as higher speeds will bring problems to cards and drives or other devices. The only exception is on servers where the speed rises to 64 MHz. Specific interrupts are assigned to each device by the system software to improve their performance. When sharing an interrupt port there must be a method to tell the device if the interrupt is for itself or other specific device that shares the IO port. For this to happen the PCI is installed with special hardware that support such a process. PCI also supports bus mastering by covering the physical size in the bus. This includes wire spacing, electrical characteristics, bus timing and protocols.
PCI has the ability to support both 32-bit and 64-bit data paths running at a clock speed of 33MHz or 66MHz. Another new feature found in the latest versions is the adaptation of PCI to be able to signal to other form factors. These qualities make it the server expansion bus of choice. Peripheral Component Interconnect Express is the expected future replacement to Peripheral Component Interconnect and Peripheral Component Interconnect derived AGP buses. This is because despite the huge investment of energy and time in improving the speed of processors and memory little has ever been achieved with the major connection between PCI and the many devices available.