由于一个系统本身所能支持的PCI插槽有限，所以，在PCI插槽足够的情况下，我们通常采用相同的卡，把端口平均分摊到每一块多用户卡上。但在PCI插槽数不够的情况下，就一定要采用高性能的多用户卡。
但是对于路由器而言，一般路由器的瓶颈在于转发引擎的处理速率而不在于端口速率。
The bottleneck of the router is not depended on the speed of the port, but depended on by the speed of the forwarding engine.
典型的ATM输出缓冲交换结构有着理想的性能，但需要N倍端口速率的高速传送而难以实现。
The typical model of output queueing in ATM switching has ideal performance, but is difficult to realize because of the need of high speed transfer that is N times the port speed.
并提出串口通信需要考虑的问题，包括计算机端口隔离保护、通信速率与距离的关系等。
Some techniques of serial communication are presented, including isolation protection of computer port, relationship between communication speed and distance, and so on.
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