SYSTEM DATA
Overlay Manager Internal Variables
| Address |
Variable |
Description |
| 0002 |
OvrCodeList |
Overlay code segment list: 0 = no overlays |
| 0004 |
OvrHeapSize |
Minimum overlay heap size in paragraphs (16 bytes) |
| 0006 |
OvrDebugPtr |
Overlay debugger hook used by Turbo Pascal Debugger |
| 000A |
OvrHeapOrg |
Overlay buffer origin (segment address of the start of the overlay buffer) |
| 000C |
OvrHeapPtr |
Overlay buffer pointer (Used internally) |
| 000E |
OvrHeapEnd |
Stores the segment address of the end of the overlay buffer |
| 0010 |
OvrLoadList |
Loaded overlays list |
| 0012 |
OvrDosHandle |
Overlay file handle. Stores the file handle of the program’s overlay file |
| 0014 |
OvrEmsHandle |
Overlay EMS handle. Handle of overlays in expanded memory block |
Heap Internal Variables
| Address |
Variable |
Description |
| 0016 |
HeapOrg |
Points to the bottom of the heap |
| 001A |
HeapPtr |
Points to the top of the heap |
| 001E |
HeapEnd |
Points to the end of DOS memory used by programs |
| 0022 |
FreeList |
Points to the first free block in the heap |
| 0026 |
FreeZero |
??? |
| 002A |
HeapError |
Pointer to Heap Error Handler |
Exit/Error Internal Variables
| Address |
Variable |
Description |
| 002E |
ExitProc |
Pointer to application’s exit procedure list |
| 0032 |
ExitCode |
Contains the application’s exit code |
| 0034 |
ErrorAddr |
Contains the address of the statement causing a run-time error |
Program Segment Prefix
| Address |
Variable |
| 0038 |
PrefixSeg |
Stores PSP segment address setup by DOS upon loading the program.
Constants and Variables
| Address |
Variable |
| 003A |
StackLimit |
This is the lowest value the SP register can contain before it is considered a stack overflow.
I/O Function Result
| Address |
Variable |
| 003C |
InOutRes |
Stores the status of the last 1/a operation performed.
Random Number Generator
| Address |
Variable |
Description |
| 003E |
RandSeed |
Stores the built-in random number generator’s seed (LongInt) |
Miscellaneous Constants and Variables
| Address |
Variable |
Description |
| 0042 |
SelectorInc |
Number to add/subtract to increase/decrease selector by 64K |
| 0044 |
Seg0040 |
Selector for segment 0040 (ROM BIOS Workspace) |
| 0046 |
SegA000 |
Selector for segment A000 (EGA and VGA Graphics Pages) |
| 0048 |
SegB000 |
Selector for segment B000 (Monochrome Adapter video memory) |
| 004A |
SegB800 |
Selector for segment B800 (CGA Adapter video memory) |
8086 CPU Type
| Address |
Variable |
| 004C |
Test8086 |
Type of 80x86 processor the system contains:
- 0 Processor is an 8086
- 1 Processor is an 80286
- 2 Processor is an 80386 or later
8087 fCPU Type
| Address |
Variable |
| 004D |
Test8087 |
Stores the results of the 80x87 autodetection logic and coprocessor classification:
- 0 No coprocessor detected
- 1 8087 detected
- 2 80287 detected
- 3 80387 or later detected
Constantas and Variables
| Address |
Variable |
| 004E |
FileMode |
Access code to pass to DOS when typed and untyped files are opened using the Reset procedure.
Input/Output Text File Records
| Address |
Variable |
| 0050 |
Input |
| 0150 |
Output |
Standard Input and Output files setup by Turbo Pascal. Each Text file record is around 256 bytes in size.
See: Text File Type
Interrupt Vectors
| Address |
Variable |
| 0250 |
SaveInt00 |
| 0254 |
SaveInt02 |
| 0258 |
SaveInt1B |
| 025C |
SaveInt21 |
| 0260 |
SaveInt23 |
| 0264 |
SaveInt24 |
| 0268 |
SaveInt34 |
| 026C |
SaveInt35 |
| 0270 |
SaveInt36 |
| 0274 |
SaveInt37 |
| 0278 |
SaveInt38 |
| 027C |
SaveInt39 |
| 0280 |
SaveInt3A |
| 0284 |
SaveInt3B |
| 0288 |
SaveInt3C |
| 028C |
SaveInt3D |
| 0290 |
SaveInt3E |
| 0294 |
SaveInt3F |
| 0298 |
SaveInt75 |
Stores original interrupt vectors for INT 00h/02h/1Bh/21h/23h-24h/34h-3Fh/75h. Each can contain a FAR address (4 bytes).
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