Think about it, which textbook will you be asked to take out when your teacher is in class? Does xx have to be 1 or something? The keys on the keyboard are all the same, each key has a name, and you can type the corresponding words on the computer. But the computer only recognizes machine language, and it can't understand what A is and what B is, so in order to let the computer know which key we pressed, we will add one to each key on the keyboard. This code is the key value.