Physical
                                 Address 
                                 Space
                                +-----------+
                               /|           |\
                              / | I/O Page  | \
                             /  |           |  \
                            /   +-----------+   \
                           /   /|           |\   \
                          /   / |           | \   \
                         /   /  |           |  \   \
             Kernel     /   /   +-----------+   \   \    User
            Virtual    /   /    | Interrupt |\   \   \  Virtual
Address     Address   /   /     | Service   | \   \   \ Address      Address
Range   PAR  Space   / > /      | Routine   |  \   \ < \ Space  PAR  Range
+------+----+-------+ / /       |-----------+   \   \ \ +-------+----+------+
|177776|    |       |/ /        |...........|\   \   \ \|       |    |177776|
|160000| 7  |       + /         |...........| \   \   \ +       | 7  |160000|
|      |    |       |/          |...........|  \   \ < \|       |    |      |
+------+----+-------+-----------+-----------+   \   \ \ +-------+----+------+
|157776|    |       |           |...........|    \   \ \|       |    |157776|
|140000| 6  |       +---------->|...........|     \   \ +       | 6  |140000|
|      |    |       |           |...........|      \ < \|       |    |      |
+------+----+-------+           +-----------+       \ \ +-------+----+------+
|137776|    |       |           |...........|        \ \|       |    |157776|
|120000| 5  |       +---------->|... ??? ...|         \ +       | 5  |140000|
|      |    |ISREP: |           |...........|          \| ISREP:|    |      |
+------+----+-------+   120000  +-----------+           +-------+----+------+
|117776|    |       |           |           |           |       |    |157776|
|100000| 4  |       +---------->|           |<----------+       | 4  |140000|
|      |    |       |           |           |           |       |    |      |
+------+----+-------+           +-----------+           +-------+----+------+
|077776|    |       |           |           |           |       |    |157776|
|060000| 3  |       +---------->|           |<----------+       | 3  |140000|
|      |    |       |           |           |           |       |    |      |
+------+----+-------+           +-----------+           +-------+----+------+
|057776|    |       |           |           |           |       |    |157776|
|040000| 2  |       +---------->|           |<----------+       | 2  |140000|
|      |    |       |           |           |           |       |    |      |
+------+----+-------+           +-----------+           +-------+----+------+
|037776|    |       |           |           |           |       |    |157776|
|020000| 1  |       +---------->|           |<----------+       | 1  |140000|
|      |    |       |           |           |           |       |    |      |
+------+----+-------+           +-----------+           +-------+----+------+
|017776|    |200/340|           |           |           |       |    |157776|
|000000| 0  |202/   +---------->|           |<----------+       | 0  |140000|
|      |    |  ISREP|           |           |           |       |    |      |
+------+----+-------+           +-----------+           +-------+----+------+
                          ^                       ^
                          |                       |
                       Kernel                   Privileged
                       Mapping                  Mapping Modified