Hardware Reference
In-Depth Information
15-bit
Memory address
Output
register
Virtual
page
1
1 0 0 0 0 0 0 0 0 1 0 1 1 0
Page
table
Present/absent
bit
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
1
110
Input
register
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 1 0 1 1 0
20-bit virtual page
12-bit offset
32-bit virtual address
Figure 6-4.
Formation of a main memory address from a virtual address.
After a page fault has occurred, the operating system must read in the required
page from the disk, enter its new physical memory location in the page table, and
then repeat the instruction that caused the fault.
It is possible to start a program running on a machine with virtual memory
even when none of the program is in main memory. The page table merely has to
be set to indicate that each and every virtual page is in the secondary memory and
