Terminology: Memory Window, Bank and Page
          =========================================

A memory window is a range of addresses in memory where other
memory is "seen" through, such as the area &8000-&BFFF on the
BBC.

Through the memory window are banks which can be switched in,
as with the 16 banks of sideways ROM/RAM on the BBC that are
switched into the memory window at &8000-&BFFF.

Pages are different areas of memory that are switched into
banks of memory, as with the Advanced Quartermeg RAM where
multiple pages of memory can be switched into a bank of
sideways ROM/RAM.

                                 ___
                                /  /|
                               /  / |
                              /__/  |
                             /  /|  |
                            /  / |  /
           +------+        /__/  | /
           |      |       /  /|  |/
           |      |      /  / |  / pages
           |      |     /__/  | /
           |      |    /  /|  |/
           |      |   /  / |  /
           +------+--+--+--+--+--+
           |      |  |  |  |  |  |
    window |      |  |  |  |  |  |
           |      |  |  |  |  |  |
           +------+--+--+--+--+--+ 
           |      |     banks
           |      |
           |      |
           |      |
           |      |
           +------+
            memory
 
So, the *AQRPAGE <page> command is xxxPAGE as it selects a /page/
of AQR RAM to appear in the sideways bank that it is plugged into.

The *SRPAGE <bank> <page> command is xxxPAGE as it selects a /page/
of ROM/RAM to appear in the specified sideways ROM/RAM /bank/.