教程-专业英语计算机

1、计算机时读(967)PCI Express pumps up performancehe past decade, PCI has served as the dominant I/O PCs and servers, carrying data generated by micropro adapters, graphics cards and other subsystems to whicharchitecture for sors, networkit is connected.However, as the speed and capabilities of computing co

2、mponents increase,PCIs bandwidth limiions andthe inefficiencies of its parallelarchitecture increasingly havee bottlenecks to systembus architecture in whiperformance. ultipleperformance ofPCI is aadapters the PCIunidirectional parallelmust contend for availabus bandwidth. Althougherface has been im

3、proved over the years, problems with signalskew (when bits of data arrive at their destination too late), routing and the inability to lower the voltage or increase the strongly indicate t the architecture is running out ofAdditional attempts to improve its performance would be costlysignal frequenc

4、y,.andimpractical. In response, agroup of vendors, including some of thelargest and most I/O architecture I/O, or 3GIO).PCI Express is asucsfulsystem developershe industry, unveiled andubbed PCIExpress (initially called Third Generationpo-to-poswitching architecturet createsI/O (the switch links can

5、high-speed, bidirectional links betn a Cnd systemis connected to the CPU by a host bridge). Each of thesepass one or more “lanes”comprising four wirestwo for transmittingdata and two for receiving data. The design of these lanables the useof lower voltages (resulting in lowower usage), redusignal sk

6、ew, lowers costs through performance.electromagnetic emiss, eliminatessimpler design and generally improvesIn its initial implemenion, PCI Express can yield transfer speedsofof2.5G bit/sec in each direction, on each lane. By contrast, the verthe Prchitecturet is most commontoday, PCI-X 1.0, offers 1

7、Gare available in four- or x8). An x4 PCI Express cardbit/sec eight-laneprovide ashroughput. PCI Express cardsconfigurations (called x4 andcanmuch as 20G bit/sechroughput, while an x8 PCI Express cardhroughput.can offer up to 40G bit/secEarr attempts to create a new Prchitecture failed in part becau

8、se they required so many changes to the system and application software.Drivers, utilities and management applications all would have to berewritten. PCI Express developers removed the dependency on new operatingsystem support, lettingpatible drivers and applications rununchanged oI Express hardware

9、.A bus for the futureDevelopers are current servergraphics cardsworking on increasing the scalability of PCI Express. Whileand desktop systempport PCI Express adapters andwith up to eight lanes (x8), the architecture will supportas many as 32 lanes (x32)hefuture.adapters were designed to support fou

10、r part because server developers hadTheFibre Channel host buslanes instead of eight designed their systemsrequired, implementinglanes, inwith four-lane slots. As even more bandwidth isan eight-lane design potentially could double theperformance, provided there were no other bottleneckshe system.This

11、 scalability, along with the expected doubling of the speed of eachlane to 5G bit/sec, should keep PCI Express adesigners for the foreseeable future.viable solution forPCI Expressis a significant improvement ovthe new standard for PCs, serversnd is well on its wayand more. Not only can ittoinglower

12、costsand improve reliability, but it also significantly can improveperformance. Applicationch as music andstreaming,ondemand, VoIP and data storage will benefit from these improvements.PCI Express 总线性能在过去十，PCI 总线一直是 PC 机和服务器上的主流 I/O 架构，它负责将微处理器、网卡、图形卡和其他子系统生成的数据送到与它相连的。然而，随着计算的速度和能力的提高，PCI 并行架构的带宽局限

13、性和低效率越来越成为系统性能的瓶颈。PCI 是一个单向的并行总线架构，其中多个适配器必须争夺可用的总线带宽。虽然 PCI 接口的性能几年来不断得到改进，但信号偏离（数据位到达目的地太晚）、信号路由、以及电压无法降低或频率更高时就不能正常工作等问题，无不表明该架构走到了尽头。改进其性能的设想代价很高，也不实际。针对此问题，一些厂商（包括最大的和最成功的系统开发商）了一个叫 PCIExpress（最初叫第三代 I/O，缩写为 3GIO）的 I/O 架构。PCIExpress 是一个点对点的交换架构，在 CPU 和系统 I/O 之间建立高速的双向链路（交换机由主桥接到 CPU）。每一个链路可以包含一

14、个或多个由四条电线组成的“通道”，其中两条线发送数据，两条线接收数据。这些通道的设计能允许在低压下使用（这样功率消耗较少）、降低电磁辐射、消除信号偏离、以及简化设计带来的成本降低，总的来说改进了性能。在其最初的实现中，PCI Express 就能保证在每个通道上双向的传输速度达到2.5G位/秒。而目前最常见的 PCI 架构版本PCI-X1.0 提供的吞吐量为 1G 位/秒。目前能得到的 PCI Express 卡为 4 通道或 8 通道的配置（叫 x4 和x8）。x4 PCIExpress 卡能提供的吞吐量达到 20G 位/秒，而 x8 PCI Express 卡能提供的吞吐量则高达 40G 位/秒。早期创建新的 PCI 架构的设想之所以失败了，是因为要求系统和应用的修改，驱动程序、例行程序和管理应用程序全都必须重写。PCI做太多Express 开发者消除了对新操作系统支持的依赖，让与 PCI 兼容的驱动程序和应用程序无需更改就能在 PCI Express 硬件上运行。未来的总线目前，开发者正在研究如何提高 PCI Express 的可扩展性。现在的服务器和台式系统支持多达 8 通道（x8）的 PCIExpress 卡和图形卡，而将来该架构能支持多达 32 通道（x32）。第一个光纤通道的主总线适配器设计成支持 4 通道，不是 8 通道，部分原因是由于服务