Peripheral Component Interconnect(PCI) slots are such an integral part of a computer's architecture that most people take them for granted. For years, PCI has been a versatile, functional way to connectsound, video and network cards to amotherboard.
But PCI has some shortcomings. Asprocessors,video cards, sound cards and networks have gotten faster and more powerful, PCI has stayed the same. It has a fixed width of 32bitsand can handle only 5 devices at a time. The newer, 64-bit PCI-X bus provides more bandwidth, but its greater width compounds some of PCI's other issues.
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A new protocol calledPCI Express(作为PCIe)消除了很多缺点,亲vides more bandwidth and is compatible with existing operating systems. In this article, we'll examine what makes PCIe different from PCI. We'll also look at how PCI Express makes a computer faster, can potentially add graphics performance, and can replace theAGPslot.
High-Speed Serial Connection
In the early days of computing, a vast amount of data moved overserialconnections. Computers separated data into packets and then moved thepacketsfrom one place to another one at a time. Serial connections were reliable but slow, so manufacturers began usingparallelconnections to send multiple pieces of data simultaneously.
It turns out that parallel connections have their own problems as speeds get higher and higher -- for example, wires can interfere with each other electromagnetically -- so now the pendulum is swinging back toward highly-optimized serial connections. Improvements to hardware and to the process of dividing, labeling and reassembling packets have led to much faster serial connections, such asUSB 2.0andFireWire.
PCI Express is a serial connection that operates more like a network than abus. Instead of one bus that handles data from multiple sources, PCIe has a switch that controls several point-to-point serial connections. (SeeHow LAN Switches Workfor details.) These connections fan out from the switch, leading directly to the devices where the data needs to go. Every device has its own dedicated connection, so devices no longer share bandwidth like they do on a normal bus. We'll look at how this happens in the next section.
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