ACT apricot - Page 244

GUIDE TO THE BIOS
GLOBAL DATA AREA
This area stores changing data values that can be accessed
and changed by
any part of the BIOS or operating system.
Initial default values are placed
into this area at boot-up
time,
some of them remain unchanged as pseudo-constants,
but others are constantly changing to dictate the current
state of the machine software and hardware. For example,
the default disk drive number is stored here which has to be
accessed by
the BIOS and MS-DOS, but can be changed at
any time. This is also the flags area, containing things such
as the "Is the calculator switched on?" flag.
BIOS HEAP AND STACK
This area should never be changed by the user, asi t
contains
the work space that the BIOS uses in every
operation.
The main program stack is here, along with the
heap workspace. It should be noted that the BIOS Stack
Segment and Data Segment are located in this area.
MS-DOS 2.0
,/
This area of memory is reserved for MS-DOS. It contains
the code, stack and all the constant area that MS-DOS 2.0
uses. This block of memory should under no circumstances
be changed by the user. No documentation is (or will be)
available as to its contents or layout.
USER RAM
This is where all the user programs are loaded and
executed from. The memory is upward vectored, and up to
the maximum Apricot address space of 896K may be used.
The program area can be divided by the user into a
self-contained Data,
Stack and Code segments. Essentially,
this area can be used at the user's discretion, and the BIOS
places no limits on (memory permitting) how much code
and/ or data is stored here.