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The Peripheral Component Interconnect, or PCI Standard (in practice almost always shortened to PCI), specifies a computer bus for attaching peripheral devices to a computer motherboard. These devices can take any one of the following forms:
* An integrated circuit fitted onto the motherboard itself, called a planar device in the PCI specification.
* An expansion card that fits into a socket.
Versions Card
32-bit, 33 MHz (added in Rev. 2.0)
64-bit, 33 MHz (added in Rev. 2.0)
32-bit, 66 MHz (3.3 V only, added in Rev. 2.1)
64-bit, 66 MHz (3.3 V only, added in Rev. 2.1)
Slot
32-bit, 5 V
32-bit, 3.3 V
64-bit, 5 V
64-bit, 3.3 V
PCI provides two separate 32-bit or 64-bit address spaces corresponding to the memory and I/O port address spaces of the x86 processor family. Addresses in these address spaces are assigned by software. A third address space, called the PCI Configuration Space, which uses a fixed addressing scheme, allows software to determine the amount of memory and I/O address space needed by each device. Each device can request up to six areas of memory space or I/O port space via its configuration space registers. Devices are required to follow a protocol so that the interrupt lines can be shared. The PCI bus includes four interrupt lines, all of which are available to each device. PCI bridges (between two PCI buses) map the four interrupt traces on each of their sides in varying ways. Some bridges use a fixed mapping, and in others it is configurable. Later versions of PCI allow (and in the latest versions require) 3.3V slots (keyed differently) on motherboards and allow for cards that are either double keyed for both voltages or even 3.3V only. PCI 2.2 allows for 66 MHz signalling (requires 3.3 volt signalling) (peak transfer rate of 533 MB/s) PCI 2.3 permits use of 3.3 volt and universal keying, but does not allow 5 volt keyed add in cards. PCI 3.0 is the final official standard of the bus, completely removing 5-volt capability.
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