15 Protected Mode Tutorial

An excellent set of programs have been written by Alexei A Founze and can be downloaded from his website or get that from here.

To run these set of programs, you'll need a system with the following configuration.

• 80386 or a better CPU
• DOS 5.0+ or Windows 9x in MSDOS mode (NOT DOS box)
• Absence of drivers such as EMM386 (and preferably HIMEM.SYS)
• Around 2MB RAM
• VGA card / SVGA card.

The following is a brief description of each of the programs:

1. Switches to PMode and back to real mode using CR0.
2. Sets up GDT, goes to PMode, prints "Hello from PMode!" and goes back.
3. The IDT is setup for software ISR (Int 20h) and divide by zero exception (Int 0). The prorgam shows work of these handlers.
4. The same GDT as before, IDT is setup for all exceptions, you may now see type and address of an exception.
5. The same GDT as before, almost the same IDT as in TUT04. Two IDT entries and IRQ handlers are added - IRQ0 (timer) and IRQ1 (keyboard). It reprograms the PIC in order to handle IRQs in Protecte Mode.
6. Almost the same as 5. Task switching is added.
7. Multitasking example.
8. Demo of page translation.
9. This tutorial is a bit different from the seventh one. It doesn't use TSS for task switchings. It uses stack-based switching instead.
10. This tutorial shows Big/Unreal Mode - how to access 4GB of memory without switching to protected mode.
11. It's almost the same as 7. The only difference is that the tasks are 32-bit.
12. Same as 11 except that two LDTs are added for each PL3 task.
13. Multitasking. First time we run a Virtual 8086 machine here.
14. Advanced V86 stuff. A software Int nn is now supported for V86 tasks.
15. A working V86 monitor - similar to a DOS box.
16. The same V86 monitor. Quite a few changes (Int 1 - single-step trap is now passed to V86 task).