In general the computer responds to an interrupt by storing the information about the current state of the running program; storing information to identify the source of the interrupt; and invoking a first-level interrupt handler. This is usually a kernel level privileged process that can discover the precise cause of the interrupt (e.g. if several devices share one interrupt) and what must be done to keep operating system tables (such as the process table) updated. This first-level handler may then call another handler, e.g. one associated with the particular device which generated the interrupt.
2. Under MS-DOS, nearly synonymous with "system call" because the OS and BIOS routines are both called using the INT instruction (see interrupt list) and because programmers so often have to bypass the operating system (going directly to a BIOS interrupt) to get reasonable performance.