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CARTRIDGE B: 8K

Locations 32768 to 40959 ($8000 to $9FFF) are used by the right
cartridge (Atari 800 only), when present. When not present, this RAM
area is available for use in programs. When the 8K BASIC cartridge is
being used, this area most frequently contains the display list and screen
memory. As of this writing, the only cartridge that uses this slot is
Monkey Wrench from Eastern House Software.

It is possible to have 16K cartridges on the Atari by either combining
both slots using two 8K cartridges or simply having one with large
enough ROM chips and using one slot. In this case, the entire area from
32768 to 49151 ($8000 to $BFFF) would be used as cartridge ROM.

Technically, the right cartridge slot is checked first for a resident
cartridge and initialized, then the left. You can confirm this by putting
the Assembler Editor cartridge in the right and BASIC in the left slots.
BASIC will boot, but not the ASED. Using FRE(0), you will see,
however, that you have 8K less RAM to use; and PEEKing through this
area will show that the ASED program is indeed in memory, but that
control was passed to BASIC. Control will pass to the ASED cartridge if
the cartridges are reversed. This is because the last six bytes of the
cartridge programs tell the OS where the program begins -- in both
cases, it is a location in the area dedicated to the left cartridge. The six
bytes are as follows:

Byte                                     Purpose
Left (A)                     Right(B)
49146 ($BFFA)             40954 ($9FFA)  Cartridge start address (low byte)
49147 ($BFFB)             40955 ($9FFB)  Cartridge start address (high byte)
49148 ($BFFC)             40956,($9FFC)  Reads zero if a cartridge is
     inserted, non-zero when no cartridge is present. This information
     is passed down to the page zero RAM: if the A cartridge is plugged
     in, then location 6 will read one; if the B cartridge is plugged in,
     then location 7 will read one; otherwise they will read zero.
49149 ($BFFD)             40957 ($9FFD)  Option byte. If BIT 0 equals one,
     then boot the disk (else there is no disk boot). If BIT 2 equals one,
     then initialize and start the cartridge (else initialize but do not
     start). If BIT 7 equals one, then the cartridge is a diagnostic
     cartridge which will take control, but not initialize the OS (else
     non-diagnostic cartridge). Diagnostic cartridges were used by
     Atari in the development of the system and are not available to the
     public.
49150 ($BFFE)             40958 ($9FFE)  Cartridge initialization address
     low byte.
49151 ($BFFF)             40959 ($9FFF)  Cartridge initialization address
     high byte. This is the address to which the OS will jump during all