Table entry format for page catalogs and page tables
| Page Frame Address 31 ... 12 Out of 20 |
Avl |
0 |
0 |
D |
A |
0 |
0 |
u/s |
r/w |
P |
D: page has been modified flag. When the processor performs a write operation on a page, the D flag of the corresponding page table entry is placed. The processor does not modify the D flag A: visited flag in the page catalog entry. When the mapped page is accessed, the corresponding page table entry is placed A; When the page table is accessed, the corresponding page catalog item A is set. U/S flag: If 1, the page is accessible to programs at any privileged level. If 0, only the (0,1,2) program is accessible. The U/S bit in the page catalog item works for all pages that it maps. R/S flag: If 1, the page strokes can be read, written, or executed. If 0, indicates that the page is read-only or executable. The r/w bit does not work when the processor is running in Superuser privileges (0,1,2). The R/W bit in the page catalog item works for all pages that it maps. P flag: Used to indicate whether the table item is valid for address translation. During page conversion, if the table entry for the page directory or page table involved is invalid, an exception is caused. If P=0, the rest of the bits can be used freely by the program, except that the table entry is invalid.
