Interrupt Vector Table
On the x86 architecture, the Interupt Vector Table (IVT) is a table that specifies the addresses of all the 256 interrupt handlers used in real mode. Although it is also called IDT, it usually goes by the name of IVT to avoid confusions realted with the protected mode interrupt descriptor table.
Typically, the IVT is located at 0000:0000H and is 400H bytes in size, 4 bytes for each interrupt. Although the default address can be changed using the LIDT on newer CPUs, this is usually not done because it is both inconvenient and incompatible with other implementations and/or older software (e.g. MS-DOS programs). However, note that the code must remain in the first MiB of RAM.