4 ms·

Also there were two groups of interrupts, IIRC: DOS interrupts and BIOS interrupts. BIOS ones were lower level and I guess some of the DOS interrupts used some

by vram22 9y ago

Also there were two groups of interrupts, IIRC: DOS interrupts and BIOS interrupts. BIOS ones were lower level and I guess some of the DOS interrupts used some BIOS ones. I remember a friend using BIOS interrupts to write a program to format a floppy disk and we sat there watching the drive make sounds as it did it.

webtechgal 9y ago
> using BIOS interrupts to write a program to format a floppy disk and we sat there watching the drive make sounds... There used to be a virus/trojan that would execute the floppy drive head re-calibration interrupt (BIOS) in an infinite loop to cause the head alignment to go out of whack, rendering the drive defunct.
- vram22 9y ago
  The things people will do ...
int_19h 9y ago
There were four broad groups: CPU interrupts - handlers for CPU errors like division by zero (0h) or overflow (4h). IRQ interrupts - handlers for hardware events; e.g. hardware timer (8h) or keyboard (9h). BIOS interrupts - for BIOS-implemented syscalls; e.g. video output (10h) or sector-oriented disk I/O (13h). Also callbacks to be invoked by BIOS, like the aforementioned 1Ch for configurable timer. DOS interrupts - for DOS-implemented syscalls; mostly this was 21h with actual syscall ID in the register. This is where you got things like file-oriented I/O, and some basic memory management. And then there was "everything else", meaning things installed by third party TSRs and drivers. For example, 33h for the Microsoft mouse driver (which all other mouse drivers promptly copied, so it became the de facto standard mouse API in DOS), or 3Eh for Borland's software floating point emulator. Of these, only the first two are actually "special" as far as hardware is concerned - the rest is just convention.
- vram22 9y ago
  Interesting, didn't know that there were 4 groups. I do remember INT 21H and setting a value in a register to specify what syscall you want run. Turbo Pascal had some support for assembly and even register handling, IIRC, so you could write such low-level programs in it. Also had absolute memory addressing which could be used for anything where you need to manipulate fixed, known memory addresses, such as video RAM.

by vram22 9y ago

webtechgal 9y ago

> using BIOS interrupts to write a program to format a floppy disk and we sat there watching the drive make sounds... There used to be a virus/trojan that would execute the floppy drive head re-calibration interrupt (BIOS) in an infinite loop to cause the head alignment to go out of whack, rendering the drive defunct.

vram22 9y ago
The things people will do ...

int_19h 9y ago

There were four broad groups: CPU interrupts - handlers for CPU errors like division by zero (0h) or overflow (4h). IRQ interrupts - handlers for hardware events; e.g. hardware timer (8h) or keyboard (9h). BIOS interrupts - for BIOS-implemented syscalls; e.g. video output (10h) or sector-oriented disk I/O (13h). Also callbacks to be invoked by BIOS, like the aforementioned 1Ch for configurable timer. DOS interrupts - for DOS-implemented syscalls; mostly this was 21h with actual syscall ID in the register. This is where you got things like file-oriented I/O, and some basic memory management. And then there was "everything else", meaning things installed by third party TSRs and drivers. For example, 33h for the Microsoft mouse driver (which all other mouse drivers promptly copied, so it became the de facto standard mouse API in DOS), or 3Eh for Borland's software floating point emulator. Of these, only the first two are actually "special" as far as hardware is concerned - the rest is just convention.

vram22 9y ago
Interesting, didn't know that there were 4 groups. I do remember INT 21H and setting a value in a register to specify what syscall you want run. Turbo Pascal had some support for assembly and even register handling, IIRC, so you could write such low-level programs in it. Also had absolute memory addressing which could be used for anything where you need to manipulate fixed, known memory addresses, such as video RAM.