A pcie device has its own direct connection a point

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Unformatted text preview: e carries those 32 bits. You’d think that 32 are better than one, correct? Well, first of all, PCIe doesn’t share the bus. A PCIe device has its own direct connection (a point-to-point connection) to the Northbridge, so it does not wait for other devices. Plus, when you start going really fast (think gigabits per second), getting all 32 bits of data to go from one device to another at the same time is difficult, because some bits get there slightly faster than others. That means you need some serious, high-speed checking of the data when it arrives to verify that it’s all there and in good shape. Serial data doesn’t have this problem, as all of the bits arrive one after the other in a single stream. When data is really going fast, a single point-to-point serial connection is faster than a shared 32-wire parallel connection. And boy howdy, is PCIe ever fast! A PCIe connection uses one wire for sending and one for receiving. Each of these pairs of wires between a PCIe controller and a device is called a lane. Each direction of a lane runs at 2.5 Gbps, or 5 Gbps with PCIe 2.0. Better yet, each point-to-point connection can use 1, 2, 4, 8, 12, 16, or 32 lanes to achieve a maximum theoretical bandwidth of 320 Gbps. The effective data rate drops a little bit because of the encoding scheme—the way the data is broken down and reassembled—but full duplex data throughput can go up to a whopping 16 Gbps on a ×16 connection. The most common PCIe slot is the 16-lane (×16) version most commonly used for video cards, as shown in Figure 8-12. The first versions of PCIe motherboards used a combination of a single PCIe ×16 slot and a number of standard PCI slots. (Remember, PCI is designed to work with other expansion slots, even other types of PCI.) There is also a small form factor version of PCI Express for mobile computers called PCI Express Mini Card. NOTE When you talk about the lanes, such as ×1 or ×8, use “by” rather than “ex” for the multiplication mark. So “by 1...
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This note was uploaded on 04/27/2010 for the course COMPTIA 1201 taught by Professor N/a during the Spring '10 term at Galveston College.

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