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* W, the controls ''''W'''rite-Through' abilities of the page. If the bit is set, write-through caching is enabled. If not, then write-back is enabled instead.
* U, the ''''U'''ser\Supervisor' bit, controls access to the page based on privilege level. If the bit is set, then the page may be accessed by all; if the bit is not set, however, only the supervisor can access it.
* R, the ''''R'''ead/Write' permissions flag. If the bit is set, the page is read/write. Otherwise when it is not set, the page is read-only.
* P, or ''''P'''resent', determines if the page is actually in physical memory at the moment. For example, when a page is swapped out, it is not in physical memory and therefore not 'Present'. If a page is called, but not present, a page fault will occur, and the OS should handle it. (See below.)
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