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added Atari entry in Systems chapter

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@ -113,8 +113,8 @@ Systems:
--------
Supported systems at this time are: C64, C128, Plus/4, CBM 600/700, the newer
PET machines (not 2001), and the Apple ][ (thanks to Kevin Ruland, who did the
port).
PET machines (not 2001), Atari 8bit, and the Apple ][ (thanks to Kevin Ruland,
who did the port).
C64: The program runs in a memory configuration, where only the kernal ROM
is enabled. The text screen is expected at the usual place ($400), so
@ -138,9 +138,26 @@ PET: The startup code will adjust the upper memory limit to the installed
$8000, so on a 8032 or similar machine, 31K of memory are available to
the program.
APPLE2: The program starts at $800, and of RAM is $8E00, so 33.5K of memory
APPLE2: The program starts at $800, end of RAM is $8E00, so 33.5K of memory
(including stack) are available.
Atari: The startup code will adjust the upper memory limit to the installed
memory, considering future graphics memory usage (which is allocated
at top of RAM). The programmer can specify which graphics mode is
about to be used by defining a variable _graphmode_used, unsigned
char, to the mode value (mode values like Atari DOS, 0-31).
(Please note that graphics mode selection isn't supported in the
Atari runtime lib yet!)
In the default case the upper memory limit will be $8035 (with Basic
cartridge) and $A035 (without cartridge). This is the default which
leaves room for the biggest possible graphics mode. If only standard
text mode is used (_graphmode_used = 0), the values are $9C1F (with
Basic) and $BC1F (no cartridge).
The program starts at $1F00 (to leave room for DOS), and the free
memory values are $6135 (24K, Basic, default mode), $8135 (32K, no
Basic, default mode), $7D1F (31K, Basic, mode 0) and $9D1F (39K,
no Basic, mode 0).
These values are for a 48K or 64K machine.
Note: The above numbers do not mean that the remaining memory is unusable.
However, it is not linear memory and must be accessed by other, nonportable