: One more question.In pmode if you do not reinitialize the PIC to point at other interupts numbers what will happen when the timer sends interupt signals and the interupts are enabled?
Intel reserved interrupt table entries 0-31 for exceptions but IBM used much of that range for their first x86-based computer. Leaving the PIC's mapped how they were programmed by the BIOS would have the PIT fire an IRQ and cause the CPU to execute the handler corresponding to entry 8, which is also an exception (double fault). So how are you going to tell if your routine was called as an exception or IRQ handler? I know there is a way by asking the PIC, and EMM386 uses it, but the simplest way is to avoid the situation and remap your IRQ handlers out of the way of the exception handlers.