Interrupt vector table

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 architectures, IVTs may be implemented in architecture-specific fashions. For example, a dispatch table is one method of implementing an interrupt vector table.

This article is about the general concept. For its implementation found in x86 processors, see Interrupt descriptor table.

Interrupts are assigned a number between 0 to 255. The interrupt vectors for each interrupt number are stored in the lower 1024 bytes of main memory. For example, interrupt 0 is stored from 0000:0000 to 0000:0003, interrupt 1 from 0000:0004 to 0000:0007, and so on.

Interrupt List
Interrupt Number IVT Address Interrupt Name
0 00-03 CPU divide by zero
1 04-07 Debug single step
2 08-0B Non Maskable Interrupt (NMI input on processor)
3 0C-0F Debug breakpoints
4 10-13 Arithmetic overflow
5 14-17 BIOS provided Print Screen routine
6 18-1B Reserved
7 1C-1F Reserved
8 20-23 IRQ0, Time of day hardware services
9 24-27 IRQ1, Keyboard Interface
A 28-2B IRQ2, ISA Bus cascade services for second 8259
B 2C-2F IRQ3, Com 2 hardware
C 30-33 IRQ4, Com1 hardware
D 34-37 IRQ5, LPT2, Parallel port hardware (Hard Disk on XT)
E 38-3B IRQ6, Floppy Disk adaptor
F 3C-3F IRQ7, LPT1, Parallel port hardware
10 40-43 Video services, see note 1
11 44-47 Equipment check
12 48-4B Memory size determination
13 4C-4F Floppy I/O routines
14 50-53 Serial port I/O routines
15 54-57 PC used for Cassette tape services
16 58-5B Keyboard I/O routines
17 5C-5F Printer I/O routines
18 60-63 Points to basic interpreter in a "real" IBM PC
19 64-67 Bootstrap loader
1A 68-6B Time of day services
1B 6C-6F Services Ctrl-Break service
1C 70-73 Timer tick (provides 18.2 ticks per second)
1D 74-77 Video parameters
1E 78-7B Disk parameters
1F 7C-7F Video graphics
20 80-83 Program termination (obsolete)
21 84-87 All DOS services available through this Interrupt
22 88-8B Terminate address
23 8C-8F Ctrl-Break exit address
24 90-93 Critical error handler
25 94-97 Read logical sectors
26 98-9B Write logical sectors
27 9C-9F Terminate and stay resident routines (obsolete)
28 to 3F A0-A3 to FC-FF Reserved for DOS
40 to 4F 100-103 to 13C-13F Reserved for BIOS
50 140-143 Reserved for BIOS
51 144-147 Mouse functions
52 to 59 148-14B to 164-167 Reserved for BIOS
5A 168-16B Reserved for BIOS


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