0,1



Locations zero to 255 ($0 to $FF) are called "page zero" and have
special importance for assembly language programmers since these
locations are accessed faster and easier by the machine.
Locations zero to 127 ($0 to $7F) are reserved as the OS page zero,
while 128 to 255 ($80 to $FF) are the BASIC and the user zero page
RAM. Locations zero to 1792 ($0 to $700) are all used as the OS and (if
the cartridge is present) 8K BASIC RAM (except page six). Locations
zero to 8191 ($0 to $1FFF) are the minimum required for operation
(8K).
Locations two through seven are not cleared on any start operation.

DECIMAL        HEX            LABEL
0,1            0,1            LINZBS
     LINBUG RAM, replaced by the monitor RAM See the OS
     Listing, page 31. It seems to be used to store the VBLANK timer
     value. One user application I've seen for location zero is in a
     metronome program in De Re Atari. Also used in cross-
     assembling the Atari OS.

2,3            2,3            CASINI
     Cassette initialization vector: JSR through here if the cassette
     boot was successful. This address is extracted from the first six
     bytes of a cassette boot file. The first byte is ignored. The second
     contains the number of records, the third and fourth contain the
     low and high bytes of the load address, and the fifth and sixth
     contain the low and high bytes of the initialization address.
     Control upon loading jumps to the load address plus six for a
     multi-stage load and through CASINI for initialization. JSR
     through DOSVEC (10 and 11; $A,$B) to transfer control to the
     application.

4,5            4,5            RAMLO
     RAM pointer for the memory test used on powerup. Also used to
     store the disk boot address--normally 1798 ($706)--for the
     boot continuation routine.

6              6              TRAMSZ
     Temporary Register for RAM size; used during powerup
     sequence to test RAM availability. This value is then moved to
     RAMTOP, location 106 ($6A). Reads one when the BASIC or the
     A (left) cartridge is plugged in.

7              7              TSTDAT
     RAM test data register. Reads one when the B or the right
     cartridge is inserted.

     RAMLO, TRAMSZ and TSTDAT are all used in testing the RAM