Unlike DOS, which works under Real mode of processor, Windows works under protected mode of the processor. In protected mode the registers are 32-bit long and are often known as extended registers For example, corresponding to the AX, BX, CX, DX, IP registers of real mode, there exist 32-bit registers called EAX, EBX, ECX, EDX and EIP under protectedAlso under protected mode interrupt handling is a little different. The interrupt vector table is no longer kept at a low address space. Instead it is replaced by another table Interrupt Descriptor Table (IDT) which is kept anywhere in physical memory. A dedicated register called IDTR holds the address of the IDT. While booting Windows constructs the table in available physical memory and stores its address in the IDTR register via a special instruction called SIDT (Store IDT). Windows fills the IDT with addresses of various kernel routines.
Correct me if I'm wrong, but if I remember correctly, Ring 3 applications(which is what all user-designed programs that run in Windows are, unless they are a device driver or VxD) can't even use the interrupts in Windows.
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