最好的做法是计算一下栏1到6中的每张卡片，然后将识别标记添加到栏73到80上。
The best practice was to number each card in columns 1 to 6, and add an identification mark on columns 73 to 80.
对每一个非初始化堆指针存储，卡片标记算法可以只增加两到三个机器指令，并要求在小的收集时对所有脏卡片上的对象进行扫描。
Card marking algorithms can add as little as two or three machine instructions per non-initializing heap pointer store, and entails scanning any objects on dirty CARDS at minor collection time.
卡片标记有几项开销——卡片映射所需的额外空间、对每一个指针存储所做的额外工作，以及在垃圾收集时做的额外工作。
There are several costs to card marking - additional space for the card map, additional work to be done on each pointer store, and additional work to be done at garbage collection time.
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