Usage of the Dirty and Accessed Bits
A page of information in memory usually originates on mass storage and is copied into memory by the OS's Page Fault handler when a program requires access to one or more locations within the page. Whenever the processor accesses a page, it automatically sets the A (Accessed) bit in the corresponding PTE = 1. On a write to any location within a page, the processor also automatically sets the D (Dirty) bit = 1. Once set, it's the programmer's responsibility to clear the bits (the processor will not clear them). A better name for the Dirty bit would be the Modified bit. When set to one, it indicates that the copy of the page in memory is no longer the same as the original page on mass storage. Of the two, the ...
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