Development of the PCI bus began in 1990 headed by Intel’s Architecture Development lab. Once completed, this product quickly became one of the top choices in server expansion devices. Intel continued to work on the PCI, making improvements and adaptations and now offers the more recent PCI Express. Recently manufactured computers and motherboards contain PCI Express ports rather than the original model, but both are still functional.
The basic function of a PCI bus is to connect peripheral devices to the central processing unit, or CPU, in order to transfer data. PCI video cards, for example, are used to transfer the high volume of data required to process modern graphics and other media. In order to transfer this data, the address must first be decoded. The address of a data transfer might more simply be explained as the sort of “To” and “From” lines you would find on a letter. This information lets the PCI bus know the target for the information and which device has initiated the request. Once the address has been decoded, the PCI bus can then begin the transaction by entering the data phase.
The data phase of a transfer may actually come in bursts of multiple data phases during which the information is interpreted. Once all of the data has been transferred, either the iniator or the target sends a request that the burst end once the current data phase is completed. Some PCI busses have limited memory and can only support bursts of a certain length, but many of the newer models have increased capacity. Once a transfer has been completed, the PCI bus typically enters a brief idle cycle, though in some circumstances the bus is permitted to move directly into the next transfer. This is possible in cases where the initiator of the transaction is the same or if the initiator still has permission to use the PCI bus.
With a 64-bit data path, the PCI video card is able to increase the data transaction speed between the computer and external devices, making it easy to enjoy enhanced graphics on your computer. The PCI bus can run at different speeds, but at 66MHz it is able to achieve its highest rate of data transfer. This feature, among others, contributes to the PCI’s displacement of its predecessors the ISA and VESA local bus, and it will continue to be developed so that users can continue to enjoy enhanced graphics on their personal PCs.