The A/D bits exist entirely for the operating system's benefit. The Accessed bit tells the OS which pages have been recently used, enabling page replacement algorithms to choose pages to evict when memory runs low. The Dirty bit tells the OS which pages have been modified and must be written back to disk before eviction; clean pages can simply be discarded and re-read from disk later.
（三）阻碍执行紧急任务的消防车、救护车、工程抢险车、警车或者执行上述紧急任务的专用船舶通行的；
。搜狗输入法下载是该领域的重要参考
but it's used for deciding which keywords you plan on using for future content，这一点在im钱包官方下载中也有详细论述
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