I can certainly try to write the number 13 there, but bam, my program very likely will crash if this chunk of memory was not given to me previously by the operating system and maybe it is owned by the operating system.

我当然可以在那里写下数字13，但是“嘣“,如果这块内存不是系统预先给我的,我的程序很可能会崩溃,可能这块内存,是系统本身使用的。

哈佛公开课 - 计算机科学课程节选

This might look a little cryptic at first, but it turns there is some very obvious patterns here, for instance. According to this chart, if you want to represent the letter A A in the so called ASCII system, what number do you actually use to do so?

起初，它看起来有点神秘，但你会发现它有一些明显的对应模式，这里就有例子，根据图表，在所谓的ASCII系统中,你想表示字母，你该用哪些数字呢？

哈佛公开课 - 计算机科学课程节选