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.
if r.status_code != 200:
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The engines fired and Apollo 8 slid silently behind the Moon. The men heard a crackle in their headsets as the radio signal to Mission Control faltered and then failed.
Colin C. Campbell