cpu與外設(shè)之間的種種不匹配，速度不匹配薯演，緩沖撞芍，信號(hào)電平不同等等。所以必須有專門(mén)的代理來(lái)處理IO事件跨扮。輸入輸出控制中心（ICH,I/O controller hub）,也就是南橋芯片勤庐。
I/O Controller Hub (ICH) is a family of Intel southbridge microchips used to manage data communications between a CPU and a motherboard, specifically Intel chipsets based on the Intel Hub Architecture. It is designed to be paired with a second support chip known as a northbridge. As with any other southbridge, the ICH is used to connect and control peripheral devices.
南北橋的作用如下圖
南北橋
IO端口設(shè)計(jì)之初，就被設(shè)計(jì)成要通過(guò)寄存器的方式同cpu進(jìn)行通信好港，其內(nèi)部有專門(mén)用于數(shù)據(jù)交換的寄存器，只不過(guò)這些寄存器在IO接口之中米罚，為了區(qū)別cpu內(nèi)部的寄存器钧汹，IO端口中的寄存器被稱作端口。
in al,dx
in ax,dx
//dx寄存器中是端口號(hào)录择，表示從端口號(hào)中讀取數(shù)據(jù)
out dx,al;
out dx,ax;
//dx中存儲(chǔ)端口號(hào)拔莱，表示向端口中
