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.
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，详情可参考雷电模拟器官方版本下载
目前，美国注册游艇约为1167万艘，年新增约30万艘，其中80%为入门级产品，价格仅数万美元。欧洲则在高端超级游艇领域占据全球主导地位，形成“大众入门+中端休闲+顶级奢华”的分层市场结构。需求基础广泛，因此抗周期能力强。
Фото: Hannah Mckay / Reuters