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On x86 CPUs, when an interrupt occurs, the ISR to call is found by looking it up in a table of ISR starting-point addresses (called "interrupt vectors") in memory: the Interrupt vector table (IVT). An interrupt is invoked by its type number, from 0 to 255, and the type number is used as an index into the Interrupt Vector Table, and at that ...
An interrupt vector table (IVT) is a data structure that associates a list of interrupt handlers with a list of interrupt requests in a table of interrupt vectors. Each entry of the interrupt vector table, called an interrupt vector, is the address of an interrupt handler (also known as ISR). While the concept is common across processor ...
The interrupt descriptor table (IDT) is a data structure used by the x86 architecture to implement an interrupt vector table. The IDT is used by the processor to determine the memory addresses of the handlers to be executed on interrupts and exceptions. The details in the description below apply specifically to the x86 architecture.
The BIOS typically sets up a real mode interrupt handler at this vector that provides video services. Such services include setting the video mode, character and string output, and graphics primitives (reading and writing pixels in graphics mode).
INT 13h is shorthand for BIOS interrupt call 13 hex, the 20th interrupt vector in an x86-based (IBM PC-descended) computer system.The BIOS typically sets up a real mode interrupt handler at this vector that provides sector-based hard disk and floppy disk read and write services using cylinder-head-sector (CHS) addressing.
At boot time, all BIOS services are available, and the memory below address 0x00400 contains the interrupt vector table. BIOS POST has initialized the system timers, interrupt controller(s), DMA controller(s), and other motherboard/chipset hardware as necessary to bring all BIOS services to ready status.
Load IDTR (Interrupt Descriptor Table Register) from memory. [ b ] The IDTR controls not just the address/size of the IDT ( interrupt Descriptor Table ) in protected mode , but the IVT (Interrupt Vector Table) in real mode as well.
For example, INT 13H will generate the 20th software interrupt (0x13 is nineteen (19) in hexadecimal notation, and the count starts at 0), causing the function pointed to by the 20th vector in the interrupt table to be executed. INT is widely used in real mode. In protected mode, INT is a privileged instruction. [1]