Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Interrupt descriptor table
open-in-new
<p>The interrupt descriptor table (IDT) is a data structure used by the <a href="/facts/X86/Kypq5fgu">x86</a> architecture to implement an <a href="/facts/Interrupt_vector_table/wq6sxJTo">interrupt vector table</a>. The IDT is used by the processor to determine the memory addresses of the handlers to be executed on <a href="/facts/Interrupts/Mm6C4rpc">interrupts</a> and <a href="/facts/Exception_handling/VrJxgb9r">exceptions</a>. </p><p>The details in the description below apply specifically to the x86 architecture. Other architectures have similar data structures, but may behave differently. </p><p>The IDT consists of 256 <a href="/facts/Interrupt_vector/wq6sxJTo">interrupt vectors</a> and the use of the IDT is triggered by three types of events: processor exceptions, hardware interrupts, and software interrupts, which together are referred to as <i>interrupts</i>: </p> <ul><li>Processor exceptions generated by the CPU have fixed mapping to the first up to 32 interrupt vectors. While 32 vectors (0x00-0x1f) are officially reserved (and many of them are used in newer processors), the original 8086 used only the first five (0-4) interrupt vectors and the IBM PC IDT layout did not respect the reserved range.</li> <li>Hardware interrupt vector numbers correspond to the hardware IRQ numbers. The exact mapping depends on how the Programmable Interrupt Controller such as <a href="/facts/Intel_8259/Y5FhqM6G">Intel 8259</a> is <a href="/facts/Intel_8259/Y5FhqM6G">programmed</a>. While Intel documents IRQs 0-7 to be mapped to vectors 0x20-0x27, IBM PC and compatibles map them to 0x08-0x0F. IRQs 8-15 are usually mapped to vectors 0x70-0x77.</li> <li>Software interrupt vector numbers are defined by the specific runtime environment, such as the IBM PC BIOS, DOS, or other operating systems. They are triggered by software using the <a href="/facts/INT_(x86_instruction)/vb5qaNIR">INT</a> instruction (either by applications, device drivers or even other interrupt handlers). For example, IBM PC <a href="/facts/BIOS/AYYPUogS">BIOS</a> provides video services at the vector 0x10, <a href="/facts/MS-DOS/fVrrz1uN">MS-DOS</a> provides the <a href="/facts/DOS_API/MTvtV65u">DOS API</a> at the vector 0x21, and <a href="/facts/Linux/9FvCKSTq">Linux</a> provides the syscall interface at the vector 0x80.</li></ul>