Physical
                                Address space
                               +-------------+
                              /|             |\
                             / | I/O Page    | \
                            /  |             |  \
                           /   +-------------+   \
                          /   /|.............|\   \
                         /   / |.............| \   \
                        /   /  |.............|  \   \
             Kernel    /   /   |.............|   \   \    User
            Virtual   /   /    |.............|    \   \  Virtual
Address     Address  /   /     |.............|     \   \ Address      Address
Range   PAR  Space  / > /      |.............|      \ < \ Space  PAR  Range
+------+----+------+ / /       |.............|       \ \ +------+----+------+
|177776|    |      |/ /        |.............|        \ \|      |    |177776|
|160000| 7  |      + /         |.............|         \ +      | 7  |160000|
|      |    |      |/          |.............|          \|      |    |      |
+------+----+------+-----------+-------------+-----------+------+----+------+
|157776|    |      |           |             |           |      |    |157776|
|140000| 6  |      +---------->|             |<----------|      | 6  |140000|
|      |    |      |           |             |           |      |    |      |
+------+----+------+           +-------------+           +------+----+------+
|137776|    |      |           |  Interrupt  |           |      |    |157776|
|120000| 5  |      +---------->|  Service    |<----------|ISREP:| 5  |140000|
|      |    |      |           |  Routine    |           |      |    |      |
+------+----+------+   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|    |      |           |             |           |      |    |157776|
|000000| 0  |      +---------->|             |<----------|      | 0  |140000|
|      |    |      |           |             |           |      |    |      |
+------+----+------+           +-------------+           +------+----+------+
                        ^                           ^
                        |                           |
                     Kernel                       User
                     Mapping                      Mapping