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→Page Directory: cleared up some wording
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U, the user\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 read and write permissions flag. If the bit is not set, the page is
P, or 'Presence', determines if the page is actually in physical memory at the moment. (eg. if a page only exists on the hard drive, it is not in physical memory.) 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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