what is the difference between IVT and IDT?

Question

On Linux system, what is the difference between Interrupt Vector Table (IVT) and Interrupt Descriptor Table (IDT) ?

Answer 1

Interrupt Processing in Real Mode In real mode, the lower 1K of memory holds a data structure known as the Interrupt Vector Table (IVT). There are nominally 256 entries in this table. (Since the 80286, the IVT is not required to have 256 entries or start at physical address 0. The base and address and length of the IVT are determined by looking at the I**nterrupt Descriptor Table Register**.) Each entry contains a far pointer to an Interrupt Service Routine. Any type of interrupt routes to the appropriate Interrupt Service Routine through this table. The processor indexes the interrupt number in this table; pushes current CS, IP, and flags on the stack; and calls the far pointer specified in the IVT. The handler processes the interrupt and then executes an IRET instruction to return control to the place where the processor executed at the time of the interrupt.

Interrupt Processing in Protected Mode In protected mode, interrupts are handled in a similar way as real mode. The Interrupt Descriptor Table (IDT) does what the IVT does in real mode. IDT consists of an array of 8-byte segment descriptors called gates. The Interrupt Descriptor Table Register (IDTR) holds the base address and the limit of IDT. The IDT must exist in physical memory and should never swap out to virtual memory. This is because if an interrupt were to occur while the IDT were swapped out, the processor would generate an exception, requiring the IDT to get the handler for handling this exception, and so on until the system crashed. The gates in the IDT can consist of three types: interrupt gates, trap gates, and task gates. We won�t dwell on the details of the trap and task gates. For further information, refer to Intel processor documentation.

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