See Section 4 for a general discussion of memory dynamics and section 7 for details of system initialization.
A1 MEMLO [02E7,2] -- User-free memory low address
MEMLO contains the address of the first location in the free memory region. The value is established by the OS during power-up and system reset initialization and is never altered by the OS thereafter.
A2 MEMTOP [02E5,2] -- User-free memory high address
MEMTOP contains the address of the first non-useable memory location above the free memory region. The value is established by the OS during power-up and system reset initialitation; and then is re-established whenever the display is opened, based upon the requirements of the selected graphics mode.
A3 APPMHI [000E,2] -- User-free memory screen lower limit
APPMHI is a user-controlled variable that contains the address within the free memory region below which the Display Handler cannot go in setting up a display screen. This variable is initialized to zero by the OS at power-up.
A4 RAMTOP* [006A,1] -- Display Handler top of RAM address (MSB)
RAMTOP permanently retains the RAM top address that was contained in TRAMSZ (as described in N1) for the Display Handler's use. The value is set up as part of Handler initialization.
A5 RAMSIZ [02E4,1] -- Top of RAM address (MSB only)
RAMSIZ permanently retains the RAM top address that was contained in TRANSZ (as described in N1).