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In computing and communications, a switching and contention system which allows a range of terminals, with different speeds, to communicate through a number of output ports with several other devices such as computers.; 在计算(机)技术和通信技术中,一种交换和竞争系统,这种系统允许具有不同速率的一批终端机 通过一些输出端口与若干个诸如计算机的其它设备进行通信。Private Automatic Computer eXchange的缩写。参阅contention, port。