对于计算机中反复出现的IO这个概念不是很清楚，查了一下百度，除了说明是Input/Output之外，其他完全不知所云。
然后查了下维基百科，终于有了一点眉目：
Incomputing,input/outputorI/O(or, informally,ioorIO) is the communication between an information processing system, such as acomputer, and the outside world, possibly a human or another information processing system.Inputsare the signals or data received by the system and outputs are the signals ordatasent from it. The term can also be used as part of an action; to "perform I/O" is to perform aninput or output operation.
I/O devicesare the pieces ofhardwareused by a human (or other system) to communicate with a computer. For instance, akeyboardorcomputer mouseis aninput devicefor a computer, whilemonitorsandprintersareoutput devices. Devices for communication between computers, such asmodemsandnetwork cards, typically perform both input and output operations.
In computer architecture, the combination of theCPUandmain memory, to which the CPU can read or write directly using individualinstructions, is considered the brain of a computer. Any transfer of information to or from the CPU/memory combo, for example by reading data from adisk drive, is considered I/O.[1]
翻译如下：
在计算机中，输入/输出（即IO）是指信息处理系统（比如计算机）和外部世界（可以是人或其他信息处理系统）的通信。输入是指系统接收的信号或数据，输出是指从系统发出的数据或信号。这个术语可以用作某个动作的一部分：“执行I/O”就是指执行输入输出动作。
I/O设备是指用户和计算机之间沟通的硬件部分。例如，键盘或鼠标就是计算机的输入设备，显示器和打印机是输出设备。用来在计算机之间通信的设备，例如调制解调器和网卡，通常同时执行输入输出动作。
在计算机的体系结构中，CPU和主存的组合被认为是计算机的大脑，因为CPU可以直接执行单个指令读或写。任何与CPU内存组合（大脑）的信息传输，例如从硬盘读数据，都可以被称为I/O。
这个解释终于能够让我理解了。另外还有廖雪峰老师的通俗解释可以参照下：
/wiki/1016959663602400/1017606916795776
能够将概念用通俗易懂的方式解释，才是真正的高手。
