APPENDIX SEVEN
Player/Missile Graphics Memory Map
You have no doubt seen this little map in dozens of publications. It
shows you where your PM graphics are located in memory. The
problem is: what does it mean? I'll attempt to explain it below. First,
the map:

Double         One byte wide        Single
Line                                Line
Resolution                          Resolution
Offset                              Offset
         0   +-----------------+   0
             |                 |
             |     unused      |
             |      area       |
      +384   |-----------------|   +768
             |  0 | 1 | 2 | 3  |
             |    missiles     |
             |                 |
      +512   |-----------------|  +1024
             |                 |
             |    Player 0     |
             |                 |
      +640   |-----------------|  +1280
             |                 |
             |    Player 1     |
             |                 |
       +768  |-----------------|  +1536
             |                 |
             |    Player 2     |
             |                 |
       +896  |-----------------|  +1792
             |                 |
             |    Player 3     |
             |                 |
      +1024  +-----------------+  +2048

No matter where in memory you reserve your PM graphics area, the
location of the space used by the players and missiles will be offset the
same number of bytes from the beginning of the reserved area. That's
what the offset numbers represent: the number of bytes from the
beginning of the PM area where that object's graphics begin.

So, if you decide to reserve sixteen pages (4096 bytes) from the top of
your memory (40960), your PM graphics will begin at 36864.
Depending on which resolution you have chosen, the missile graphics
area will begin either 384 or 768 bytes from that location: or at 37248
and 37632 respectively. In double line resolution, you can define your
objects up to 128 bytes in length; in single line they can be 256 bytes
long.

Even if your object is only eight or ten bytes in height, the boundaries
for their placement are always the same relative offset from the top of
PM graphics memory.
This map is only eight bits -- one byte -- wide. You can see that all four
missiles share the same width byte, each using two bits for resolution.
If you combine the missiles to form a fifth player, you use this area
exactly as you would the area for any other player.

One means of moving your players vertically is to move the players
within their reserved area rather than on the screen itself. In BASIC,
this is considerably faster than having to move the player on the
screen, but it's a slow process anyway. As far as the boundaries of the
TV set are concerned, all players in both resolutions are mapped to the
entire height of the screen.

There are many good programs to create and edit PM graphics,
mentioned earlier in the Memory Map text. PM graphics are one of the
Atari's most powerful and least understood capabilities. I suggest you
read up on them and try to master their use; they're not as difficult as
they seem.