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.
Андрей Шеньшаков
。关于这个话题，Line官方版本下载提供了深入分析
Lovell, who was also part of the Apollo 8 mission, was the first man to go to the Moon twice - but never actually landed.
In achieving his dream to be a rocket scientist, he would become an American hero. But it was not going to be easy.
（五）其他扰乱电信、金融实名制管理的行为。