Rationale: Although simple x86 PC kernels often only use the 32 processor trap vectors plus 16 interrupt vectors, which set of vectors are used for hardware interrupts tends to differ greatly between kernels. Some kernels also want to use well-known vectors for efficient system call emulation, such as 0x21 for DOS or 0x80 for Linux. Some bootstrap mechanisms, such as VCPI on DOS, must determine at run-time the set of vectors used for hardware interrupts, and therefore potentially need all 256 vectors to be available. Finally, making use of the enhanced interrupt facilities on Intel SMP Standard-compliant multiprocessors generally requires use of higher vector numbers, since vector numbers are tied to interrupt priorities. For all these reasons, we felt the default IDT should be of the maximum size, even though much of it is usually wasted.